Genetics

Question 1

The mechanism of meiosis fits with which of the following descriptions?

Select one:
1. Occurs in all tissues
2. Has a short prophase
3. Produces daughter cells identical to parent cells
4. Produces diploid somatic cells
5. Includes recombination

Answer 1

Includes recombination

During the early stages of cell division in meiosis, two chromosomes of a homologous pair may exchange
segments - this is called recombination.

Question 2

A patient with schizophrenia is more likely to marry someone with a psychiatric problem or substance use.
This is termed as

Select one:
1. Consanguineous mating
2. Natural selection
3. Genetic drift
4. Pleiotropy
5. Assortative mating

Answer 2

Assortative mating

Assortative mating is a well established phenomenon noted in psychiatric genetic epidemiology

Question 3

What is the risk of Alzheimer dementia in a patient heterozygous for Apo E4 compared to those with no
apoE4 allele?

Select one:
1. Three times higher (OR=3)
2. Nine times higher (OR=9)
3. Same risk (OR=1)
4. Twenty times higher (OR=20)
5. Fifteen times higher (OR=15)

Answer 3

Three times higher (OR=3)

The dose of ApoE4 is directly proportional to the risk of dementia of Alzheimer’s type. The risk for AD is 2 to
3 times higher among first-degree relatives of patients with AD compared with nonrelatives. The genetic
factor with the highest attributable risk for AD is apolipoprotein E (APOE). The APOE gene on chromosome 19q has 3 codominant alleles, 2, 3, and 4, differing by single-base substitutions in the coding region of the gene. The ancestral allele, apoE4, is overrepresented and apoE2 is underrepresented in AD. In Caucasian subjects, the odds of AD for those homozygous for apoE4 is 14.9 times while for those who are heterozygous with one apoE3/4 is 3.2 times greater than the odds associated with apoE3 homozygosity.
Further, the mean age of onset of AD is 2 decades earlier in apoE4 homozygotes.

Question 4

Which of the following nuclear components undergo removal during splicing?

Select one:
1. Histones
2. Introns
3. Trinucleotide repeats
4. Exons
5. Transfer-RNA

Answer 4

Introns

An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final
mature RNA product of a gene

Question 5

Deletion in the paternally derived chromosome 15q11-q13 leads to which of the following disorders?

Select one:
1. Tuberous sclerosis
2. Huntington’s disease
3. Di George syndrome
4. Angelman’s syndrome
5. Prader Willi syndrome

Answer 5

Prader Willi syndrome

Though no structural differences exist between maternal and paternally inherited chromosomes in humans, there are some subtle functional differences that are increasingly being appreciated. For example, a
deletion of part of the long arm of chromosome 15 (15q11-q13) will give rise to the Prader-Willi syndrome
(PWS) if it is paternally inherited. A deletion of a similar region of the chromosome gives rise to Angelman’s
syndrome (AS) if it is maternally inherited. This may be due to differential regional expression of the
chromososmes.

Question 6

Which of the following syndromes is characterised by severe mental retardation, rocker bottom feet, low-set
ears, micrognathia and clenched hands?

Select one:
1. Trisomy 18
2. Velo cardio facial syndrome
3. Down’s syndrome
4. Patau syndrome
5. William’s syndrome

Answer 6

Trisomy 18

Edward’s syndrome is characterised by severe mental retardation and rocker bottom feet, low-set ears,
micrognathia (small jaw), congenital heart disease, clenched hands, and a prominent occiput. It is a result
of trisomy 18. It occurs at a frequency of 1:8000 and often death occurs within1 year of birth.

Question 7

Which of the following chromosomal loci codes for Catechol-O-methyl transferase (COMT) enzyme?

Select one:
1. chromosome 8q11
2. chromosome 4q11
3. chromosome 22q11
4. chromosome 11q22
5. chromosome Xq11

Answer 7

chromosome 22q11

COMT gene resides in 22q11 locus.

Question 8

An aborted foetus was found to have 69 chromosomes in each cell. Which of the following terms best
describes the abnormality?

Select one:
1. Diploid
2. Euploid
3. Haploid
4. Monoploid
5. Triploid

Answer 8

Triploid

When cells possess chromosomal numbers different from normal diploidy, they are called aneuploid cells.

Aneuploidy can occur in single numbers e.g. trisomy 21, trisomy 18, monosomy of Turner’s, etc. Very rarely,
the entire chromosome set will be present in more than two copies, so the individual may be triploid rather than diploid and have a chromosome number of 69. Triploidy and tetraploidy (four sets) result in
spontaneous abortion.

Question 9

CADASIL is associated with a mutation in which of the following genes?

Select one:
1. Dysbindin
2. LRRK2
3. Parkin gene
4. Notch3
5. COMT

Answer 9

Notch3

An unusual form of subcortical small vessel disease occurs in the rare inherited condition of CADASIL
(cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) in which a mutation in the Notch3 gene results in deposition of granular material in the walls of small arteries and
arterioles, narrowing of vessel lumens and destruction of smooth muscle cells in their walls.

Question 10

Which of the following terms describes deletion or insertion mutations that take place in multiples of triplet codons?

Select one:
1. Inframe mutations
2. Substitutions
3. Frame shift mutations
4. Transitions
5. Inversions

Answer 10

Inframe mutations

According to the effect on triplet sequence, mutations could be frame shift or in-frame. In frame shift
mutations, the deletion or insertion is not in multiples of three codons e.g. a segment of 5 bases deletion
mutations. This leads to a shift in triplet reading frame with variable results. Inframe mutation refers to
changes happening in multiples of 3 bases, with no disturbances in the actual reading frame.

Question 11

Which of the following criteria must be satisfied for a trait to be called an endophenotype?

Select one:
Must be independent of the clinical state
Must be associated with a candidate gene
All of the listed options
Must be co segregating with actual illness
Must have biological plausibility

Answer 11

All of the listed options

To be termed as an endophenotype, Gottesman suggested certain criteria to be satisfied by an identified disease marker. These are as follows: Must be associated with a candidate gene or region Must be present with a high relative risk in relatives, thus co segregating with actual illness Must be a parameter associated with disease with biological plausibility Must be independent of the clinical state (i.e. must not be a state but a trait marker) Must be heritable Must be present in relatives more often than general population.

Question 12

A young girl with learning difficulties is diagnosed to have trisomy X. Her chromosomes were karyotyped to
diagnose the genetic defect. How many Barr bodies would she have in her somatic cells?

Select one:
1. Information insufficient to answer the question
2. One
3. Two
4. None
5. Three

Answer 12

Two

X inactivation occurs very early in the development of female embryos. When an X chromosome is
inactivated, it could be visualized under the microscope as a highly condensed Barr body in the nuclei of interphase cells. All X chromosomes in a cell are inactivated except one, irrespective of original number of X chromosomes in a cell. Thus females with trisomy X will have two Barr bodies. X inactivation occurs via DNA methylation.

Question 13

Nucleosides consist of which of the following components?

Select one:
1. Phosphorylated nucleotide
2. Phosphate and nitrogenous base
3. Pentose sugar, phosphate and nitrogenous base
4. Pentose sugar and phosphate
5. Pentose sugar and nitrogenous base

Answer 13

Pentose sugar and nitrogenous base

Genetic information is stored in the form of double-stranded DNA. DNA and RNA are the most important
nucleic acids in the cellular machinery. These nucleic acids are composed of many nucleotides. Nucleotides
are phosphorylated versions of nucleosides. Each nucleoside consists of two components: A nitrogenous
base and a pentose sugar. Each strand of DNA is made up of a deoxyribose-phosphate backbone and a
series of purine (adenine (A) and guanine (G)) and pyrimidine (thymine (T) and cytosine (C)) bases of the
nucleic acid. The length of DNA is generally measured in numbers of base-pairs (bp).

Question 14

In which of the following patterns of inheritance does skipping one generation but reappearing on the next is commonly seen?

Select one:
1. Translocations
2. Mitochondrial inheritance
3. Autosomal dominant
4. X linked dominant
5. Autosomal recessive

Answer 14

Autosomal recessive

Autosomal recessive disorders manifest themselves only when an individual is homozygous for the disease
allele, i.e. both chromosomes carry the mutated gene. In this case, the parents are generally unaffected,
healthy but carriers (heterozygous for the disease allele). There is usually no family history, although the
defective gene is passed from generation to generation (skipping). The offspring of an affected person will be healthy heterozygotes unless the other parent is also a carrier. If carriers marry, the offspring have a 1 in 4 chance of being homozygous and affected and a 1 in 2 chance of being a carrier, and a 1 in 4 chance of being genetically normal. Consanguinity increases the risk. Often the abnormal gene in autosomal recessive diseases codes for enzymatic proteins.

Question 15

Which one of the following processes can inactivate a gene?

Select one:
1. Unwinding of DNA strands
2. Uncoiling of chromosome
3. Methylation
4 .Condensation
5. Crossing over

Answer 15

Methylation

DNA methylation is a source of epigenetic modifications.

Question 16

Which of the following genetic variants of Down’s syndrome shows less cognitive impairment and milder
features than other variants?

Select one:
1. Mosaicism
2. Full trisomy of chromosome 21
3. Duplication of a portion of chromosome 21
4. Both translocation and mosaicism
5. Robertsonian translocation

Answer 16

Mosaicism

Mosaics have a milder spectrum of the malformations as not all cells bear the chromosomal aberration.

Question 17

In which of the following phases of the cell cycle does a neuron remain for the longest period of its life?

Select one:
1. G1 phase
2. G0 phase
3. G2 phase
4. S phase
5. M phase

Answer 17

G0 phase

While certain cells pause or freeze the cycle temporarily and stay in G0, e.g. liver cells, neurons remain in G0 indefinitely.

Question 18

What percentage of the human genome is considered to be active with coding sequences?

Select one:
1. 20
2. 2
3. 30
4. 40
5. 10

Answer 18

2%

The proportion of coding and noncoding DNA within genomes varies widely among organisms. More than
98% of the human genome does not encode protein sequences, including most sequences within introns
and most intergenic DNA.

Question 19

Which of the following steps is NOT a part of polymerase chain reaction (PCR)?

Select one:
1. Extending primers in opposite directions
2. Vector based replication of DNA
3. Denaturing DNA by heat
4. Annealing DNA by cooling
5. Amplifying copies of DNA

Answer 19

Vector based replication of DNA

The PCR technique has three steps. A. Double-stranded genomic DNA is denatured by heat into single stranded DNA. The reaction is then cooled to favour DNA annealing, and the primers bind to their target DNA. B. DNA polymerase is used to extend the primers in opposite directions using the target DNA as a template. After one cycle, there are two copies of double-stranded DNA, after two cycles there are four
copies, and this number rises exponentially with the number of cycles. C. The cycling is set to produce
necessary number of amplifications. Note that the vector-based replication is used for DNA cloning, not
PCR.

Question 20

Which of the following pairing among nucleotides does not occur in human DNA sequences?

Select one:
1. AT pair
2. GC pair
3. TG pair
4. CG pair
5. TA pair

Answer 20

TG pair

Each strand of DNA is made up of a deoxyribose-phosphate backbone and a series of purine (adenine (A) and guanine (G)) and pyrimidine (thymine (T) and cytosine (C)) bases of the nucleic acid. The length of
DNA is generally measured in numbers of base-pairs (bp). Each nucleotide is a base joined to a sugar phosphate unit. The two strands of DNA are held together by hydrogen bonds between the bases. There
are only four possible pairs of nucleotides - TA, AT, GC and CG. TG pairing is not possible.

Question 21

Which of the following aminoacids constitute the initiation sequence of protein translation?

Select one:
1. Tyrosine
2. Isoleucine
3. Threonine
4. Valine
5. Methionine

Answer 21

Methionine

Translation includes three steps - initiation, elongation and termination. The ribosome contains two sites:
Peptidyl P site where methionine containing tRNA initially binds and aminoacyl A site where each new
incoming tRNAs with activated amino acids can bind. In elongation step, amino acids are added one by one
in a sting like fashion to produce proteins. Chain termination is signaled by one of the three codons UAA, UGA or UAG.

Question 22

Equatorial alignment of chromosomes is seen in which of the following phases of cell division?

Select one:
1. Interphase
2. Anaphase
3 .Telophase
4. Prophase
5. Metaphase

Answer 22

Metaphase

In metaphase, the chromosomes are aligned at the metaphase plate (a plane that is equally distant from
the two spindle poles) - equatorial alignment.

Question 23

In which of the following conditions chromosomal duplication is seen?

Select one:
1. Cri-du-chat Syndrome
2. Foetal Alcohol Syndrome
3 .Turner’s Syndrome
4. Reye’s Syndrome
5. Trisomy 21

Answer 23

Trisomy 21

Reye’s and FAS are not chromosomal disorders. Cri-du-chat is a deletion syndrome while Turner’s is a
monosomy with non-disjunction (no duplication).

Question 24

Which of the following phenomena takes place during interphase?

Select one:
1. Preparation for cell division
2. Cell division
3. Quiescence
4. Cell union
5. Nuclear division

Answer 24

Preparation for cell division

Cell division is a process by which cells reproduce “ here, a sequence of steps enable the replicated genetic material in a parent cell to be equally distributed to two daughter cells. Before a dividing cell enters mitosis, it undergoes a period of growth called interphase. Interphase is the ‘holding’ stage between two successive cell divisions. In this stage, the cell replicates its genetic material and organelles in preparation for division.
It is the longest phase, and all steps in cell cycle except stage (M) together constitute interphase.

Question 25

Which of the following type of Down's syndrome could be inherited with equivalent likelihood from either of the parents? Select one: 1. Monosomy 21 2. Unbalanced translocation 3. Trisomy 21 4. Mosaicism 5. Robertsonian translocation

Answer 25

Robertsonian translocation People with translocation Down syndrome can inherit the condition from an unaffected parent, either the mother or the father.

Question 26

In a family, father suffers from an autosomal dominant disease. Mother is a homozygous normal individual. Which of the following correctly describes the risk of this couple having a child with the autosomal dominant disorder? Select one: 1. It depends on the age of the father at time of birth 2. It depends on the birthorder 3. It depends on the sex of the child 4. The risk is 50% irrespective of sex 5. The risk increases with incomplete penetrance

Answer 26

The risk is 50% irrespective of sex Each cell contains two copies of all the autosomes. An autosomal dominant disorder occurs when one of the two copies has a mutation and the protein produced by the normal form of the gene cannot compensate. So the mutant allele becomes dominant over the normal allele and results in disease expression. In this case, a heterozygous individual who has two different forms (or alleles) of the same gene will manifest the disease. The offspring of heterozygotes have a 50% chance of inheriting the chromosome carrying the disease allele, and therefore also of having the disease. If both parents are heterozygous, the recurrence risk is 75%. This risk reduces with incomplete penetrance but is not affected by birth order or sex.

Question 27

Heritability of bipolar disorder is Select one: 1. 75-85% 2. 55-65% 3. 65-75% 4. 85-100% 5. 45-55%

Answer 27

75-85% The overall heritability of the bipolar disorder varies between 0.75 to 0.80.

Question 28

The number of autosomes in a human somatic cell is Select one: 1. 2 2. 22 3. 44 4. 23 5. 46

Answer 28

44 Chromosomes are cellular structures containing one linear molecule of DNA. Human cells are called diploid as they have 46 chromosomes, 23 inherited from each parent; thus there are 23 'homologous' pairs of chromosomes (22 pairs of 'autosomes' and two 'sex chromosomes'). The sex chromosomes, called X and Y, are not homologous but are different in size and shape. Males have an X and a Y chromosome; females have two X chromosomes,

Question 29

The investigation of choice used in the diagnosis of Klinefelter's syndrome is Select one: 1.Fetal topography 2. Fetal Ultrasound 3. Amniocentesis 4. Karyotyping 5. Chorionic villus sampling

Answer 29

Karyotyping A karyotyping is frequently used to confirm the diagnosis of Klinefelter's syndrome. In this procedure, white blood cells from the infant are separated from the plasma, mixed with a tissue culture medium, incubated, and checked for chromosomal abnormalities, such as the presence of an extra X chromosome. Diagnosis can also be made prenatally via chorionic villus sampling or amniocentesis tests in which fetal tissue is extracted, and the fetal DNA is examined for genetic abnormalities.

Question 30

The process by which one gene gives rise to more than one protein is Select one: 1. Inverse mutation 2. Transcription 3. Alternate splicing 4. Epistasis 5. Translocation

Answer 30

Alternate splicing In human DNA, the genetic information that includes the code for making a protein is located in fragments (exons, red boxes), which are interrupted by non-coding fragments (introns, green boxes). By the process of alternative splicing, the introns are removed, and the exons spliced together in different combinations, generating different messenger RNAs (mRNA) that are decoded (translated) into distinct proteins. In humans, it is estimated that alternative splicing occurs in more than 60% of genes, thus abolishing the one gene, one protein dogma long held in medical genetics

Question 31

A newly identified psychiatric disorder called 'somatomania' is found to be inherited in a simple Mendelian autosomal recessive fashion. If two patients with somatomania meet at a psychiatric ward, marry and give birth to two children, what are the chances (in percentage) that each child has inherited somatomania? Select one: 1. 33 2. 25 3. 100 4. 75 5. 50

Answer 31

100% In autosomal recessive disorders, children born to parents who are both diseased (not just carriers but diseased and so has homozygous recessive alleles) have 100% risk of inheritance.

Question 32

The commonest cardiac malformation seen in Down's syndrome is Select one: 1. Endocardial cushion defect 2. Pulmonary stenosis 3. Fallot's tetralogy 4. Atrial ostium secundum defect 5. Atrial stenosis

Answer 32

Endocardial cushion defect Congenital heart defects are common in Down (40-50%); they are frequently observed in patients with Down syndrome who are hospitalized (62%) and are a common cause of death in this aneuploidy in the first 2 years of life. The most common congenital heart defects are endocardial cushion defect (43%), ventricular septal defect (32%), secundum atrial septal defect (10%), tetralogy of Fallot (6%), and isolated patent ductus arteriosus (4%). PDA is seen in 16% while pulmonary stenosis in 9%.

Question 33

Which of the following genetic loci is associated with late onset senile dementia of Alzheimer's type? Select one: 1. Chromosome 1 Presenilin 2 2. Chromosome 17 tau protein 3 .Chromosome 21 Beta amyloid 4 .Chromosome 14 Presenilin 1 5. Chromosome 19 Apo E

Answer 33

Chromosome 19 Apo E Others are associated with presenile - early onset variety.

Question 34

A distraught mother whose first child is diagnosed recently with autistic disorder wants to know the relative risk of the same disorder to recur in her next child. The correct answer is Select one: 1. 3 times 2. 50 times 3 .10 times 4. 4 times 5. 100 times

Answer 34

50 times Autism is thought to be strongly genetic. Relative risk = the ratio of risk of autism occurring in a sibling of someone with autism: risk of autism occurring in someone without a sibling with autism = 50:1

Question 35

Which of the following genes is NOT implicated in schizophrenia? Select one: 1. D aminoacid oxidase 2. Dysbindin 3. Monoamine oxidase 4. Neuregulin 5. COMT

Answer 35

Monoamine oxidase MAO gene is not implicated; it is implicated in neuroticism and in anxiety disorders.

Question 36

In an attempt to find out if trichotillomania has a genetic basis, family history is collected by interviewing all possible first-degree relatives of 46 consecutive patients attending a hair disorder clinic. What type of study is this? Select one: 1. Family study 2. Gene mapping 3. Association study 4. Linkage analysis 5. Sib pair approach

Answer 36

Family study There are two types of family studies. The family history method is simple but unreliable; here psychiatric history is taken from the probands himself/herself. A comparison can be then made as to how many relatives are affected in one group compared to another. A more thorough but more time-consuming approach is the family study method. Here all available relatives are directly interviewed.

Question 37

Which of the following is true concerning a woman who has an autosomal recessive disorder but her husband is genotypically normal? Select one: 1. Only her daughters will receive the mutant gene 2. All her children would have the disease phenotype 3. None of her children will have the disease phenotype 4. All her daughters would be carriers, all her sons would have the disease 5. All her sons would be carriers, all her daughters would have the disease

Answer 37

None of her children will have the disease phenotype As all of the children will be carriers, none will have the expressed phenotype in normal circumstances

Question 38

Which of the following diagnosis is associated with a mutation in KISS1 gene? Select one: 1. Wernicke syndrome 2. Cushing syndrome 3. Williams syndrome 4. Kallmann syndrome 5. Addison syndrome

Answer 38

Kallmann syndrome Kallmann Syndrome (Hypogonadotropic hypogonadism along with anosmia, and occasionally learning difficulties) is associated with Kiss1 gene mutations. Prevalence of Kallmann syndrome is ~ 1 in 8000, M:F =5:1. X-linked recessive, autosomal dominant and autosomal recessive patterns of inheritance are observed; however, many cases are sporadic with no Mendelian inheritance pattern. A number of genes are implicated in KS, Kiss1 accounting for only a very small portion of cases.

Question 39

A 4-year-old child presents with developmental delay, growth retardation, generalised dystonia and an IQ of 60. On investigation, hyperuricaemia is noted. Which of the following is likely to be seen? Select one: 1. Insensitivity to pain 2. Progressive dementia 3. Self injurious behaviour 4 .Liver failure 5. Hair loss

Answer 39

Self injurious behaviour Repeated self-injurious behaviour is a common feature of Lesch-Nyhan syndrome in which hyperuricemia is also noted.

Question 40

Mrs. Brown gives birth to twins in her first delivery. The twins look alike with respect to their hair colour but look different with respect to the colour of iris. Which of the following statement is most likely with the available information? Select one: 1. They are dizygotic twins 2. They are monozygotic twins 3. They are concordant for iris colour 4. They are identical twins 5. They are concordant for hair colour

Answer 40

They are concordant for hair colour Two individuals are concordant if they share the same trait; if they do not share the trait, they are discordant. For a trait that is completely genetic, one would expect a concordance of 100% for MZ twins because they share all of their genes. The concordance rates for DZ twins should be only about 50%. In contrast, a trait that has no genetic basis should have equivalent concordance rates for MZ and DZ twins.

Question 41

Which of the following is responsible for dementia seen in adults with Down's syndrome? Select one: 1. Loss of genetic material corresponding to presenilin -1 2. Loss of genetic material in chromosome 21 3. Genetic material lost from chromosome 14 4. Loss of genetic material corresponding to Apoe4 5. Extra genetic material in chromosome 21

Answer 41

Extra genetic material in chromosome 21 Chromosome 21 is implicated in both Down's and Alzheimer's. The extra genetic material in trisomy causes a pathology similar to dementia.

Question 42

Serotonin transporter promoter region shows short and long allele variants as a polymorphism. Which of the following statements about polymorphisms, in general, is true? Select one: 1. Generally occur at a rate above 6% in population 2. Maintained by evolutionary processes 3. Produce a functional defect in the subject 4. Cannot be used for linkage analysis 5. Can be seen only in exons

Answer 42

Maintained by evolutionary processes Polymorphism refers to variations in genetic make-up at a particular locus noted in general, apparently healthy population. To be defined as polymorphism, the variant must occur in at least 1% of the total population and must be associated with normal (not abnormal i.e. disease-causing) expression of the final phenotype. This excludes spontaneous mutations that are random and so cannot simultaneously occur in such significant (1%) proportion of total population. ABO blood groups are good examples of polymorphism expressed in protein products of genes. It is assumed that evolutionary selection serves to maintain polymorphisms.

Question 43

Variation of a genetic code across the population without any associated overt phenotypic change is best described as Select one: 1. Mutation 2. Epigenesis 3. Polymorphism 4. Gene silencing 5. Point deletion

Answer 43

Polymorphism Polymorphisms are natural variations in a gene, DNA sequence, or chromosome that have no adverse effects on the individual and occur with fairly high frequency in the general population. Gene silencing refers to the epigenetic processes of gene regulation whereby the "switching off" of a gene takes place by a mechanism other than genetic modification. This occurs when RNA is not translated to a protein downstream.

Question 44

Which of the following is a clinical feature seen in Turner's syndrome (45X0)? Select one: 1. Webbed neck 2. Narrow chest 3. Prognathism 4. Receding hairline 5. Tall stature

Answer 44

Webbed neck Webbed neck with prominent low hairline, retrognathism, short stature and broad chest are features of Turner's.

Question 45

Which of the following is an autosomal dominant disorder? Select one: 1. Fredreich's ataxia 2. Phenylketonuria 3. Noonan's syndrome 4. Hurler's syndrome 5. Tay-sach's disease

Answer 45

Noonan's syndrome Noonan syndrome is caused by a genetic mutation and is acquired in an autosomal dominant fashion mostly or as a spontaneous mutation rarely. Noonan's syndrome is characterised by short stature, congenital heart defect and delayed mental development of varying degree. Patients with Noonan syndrome also have a characteristic appearance: short neck, cervical skin fold, low set ears, hypertelorism. Additionally lymphatic dysplasia leading to cystic hygroma and occipital fold enlargement may be seen in the fetus. The incidence is around 1:1000-2500. Mutations in the HEXA gene coding the lysosomal enzyme beta-hexosaminidase produces TaySach's disease that is common in people of Ashkenazi (eastern and central European) Jewish heritage. It is inherited in an autosomal recessive pattern. Friedreich's ataxia is an autosomal recessive disease involving the defective FXN gene, which codes for theproduction of a protein called "frataxin." In the normal version of the gene, a sequence of DNA (labeled "GAA") is repeated between 7 and 22 times. A higher number of this triplet repeat expansions produce the disease. Hurler syndrome is an autosomal recessive disease, with genetic loci at 4p16. The disease is usually caused by multiple missense and frameshift mutations which produce Alpha-L-iduronate deficiency. PKU is an autosomal recessive disorder. It is the most common genetic disease involving amino acid metabolism.

Question 46

Which of the following correctly describes gene mapping? Select one: 1. A strategy by which parental identity is established in case of disputes 2. A method by which genes are distributed during mitosis 3. A method by which genes are distributed in meiosis 4. A strategy that permits finding the chromosomal location of genes 5. A process by which ethnographic genetic distribution is studied

Answer 46

A strategy that permits finding the chromosomal location of genes Gene mapping refers to any strategy that permits finding the chromosomal location of one or more genes, often related to a disease. Genetic mapping of disease genes is a very useful method because it does not require any knowledge of a gene's function to find the chromosomal location initially. Once located then the identity of the disease gene could be dissected. Not all genetic studies are aimed at gene mapping; certain simpler designs are primarily aimed at demonstrating the presence or absence of a genetic influence in the aetiology of a disease or trait. These include family studies, twin studies, and adoption studies. Gene mapping studies involve linkage analysis, sib-pair analysis and to some extent allelic association studies.

Question 47

The best technique to detect a large sequence of DNA is Select one: 1. Electron microscopy 2. PCR 3. Southern blotting 4. Linkage study 5. Radiolabelling technique

Answer 47

Southern blotting Southern blotting was named after Edward M. Southern who developed this procedure at Edinburgh University in the 1970s. Southern blotting is designed to locate a particular sequence of DNA within a complex mixture. Fluorescent in situ hybridization (FISH) is a technique that exploits the principle of nucleic acid hybridization, in which single-stranded nucleic acids (usually DNA, sometimes RNA) interact with sufficiently similar, complementary sequences, to form hybrid complexes. This process helps to identify an unknown sequence and locate it on a given chromosome.

Question 48

Which of the following gives the value of one centiMorgan? Select one: 1. 100 base pairs of DNA 2. 1000 basepairs of DNA 3. 100% recombination frequency between two loci 4. 1% recombination frequency between two loci 5. 10 base pairs of DNA

Answer 48

1% recombination frequency between two loci Genetic distances are often expressed in centiMorgans (cM). One centiMorgan is equal to a 1% recombination frequency between two loci. One cM is approximately equal to 1 million base pairs of DNA (1 Mb).

Question 49

Lucy is Lenny's half sister. The proportion of genes that might be shared between Lucy and Lenny is Select one: 1. 50 2. 33 3. 25 4. 20 5. 12

Answer 49

50% First-degree relatives share one-half of their genes. Second-degree relatives share one-fourth, and third degree relatives share one-eighth.

Question 50

In a closed islandic population, frequency of genotype HH is 50, hh is 10 while Hh is 40. What is the gene frequency of H? Select one: 1. 14 2. 0.7 3. 70 4. 7 5. 1.4

Answer 50

0.7 Out of 200 gene copies in 100 people, H occurs 50+50+40 = 140 times. Hence gene frequency of H is 140/200 = 0.7

Question 51

Which of the following conditions is an example of aneuploidy? Select one: 1. Thalassemia 2. Huntington's disease 3. Absence seizures 4. Phenylketonuria 5. Down's syndrome

Answer 51

Down's syndrome The most common non-fatal aneuploidy is trisomy 21 or Down syndrome, affecting 1 in 800 births.

Question 52

If both parents suffer from an autosomal recessive disorder, the probability of each child being affected is Select one: 1. 1:1 2. 1:2 3. 1:4 4. 1:3 5. 1:5

Answer 52

1:1 Autosomal recessive disorders manifest themselves only when an individual is homozygous for the disease allele; i.e. both chromosomes carry the mutated gene. So if both parents suffer from a disorder, the probability of each child being affected is 100% or 1:1. If carriers marry, the offspring has a 1 in 4 chance of being homozygous and affected and a 1 in 2 chance of being a carrier, and a 1 in 4 chance of being genetically normal. Consanguinity increases the risk.

Question 53

Which of the following can be used to study the abnormalities in the candidate genes associated with schizophrenia in patients with psychosis? Select one: 1. Chromosomal count 2. Amount of methylation 3. Single nucleotide polymorphisms 4. Heterochromatin material 5. Translocation

Answer 53

Single nucleotide polymorphisms Genome-wide association studies are based on linkage disequilibrium (LD), using several hundred thousand marker single nucleotide polymorphisms or SNPs.

Question 54

When compared with the general population, the range of full-scale IQ in people with Turner's syndrome is shifted down by Select one: 1. 30 points 2. 20 points 3. 0 points 4. 40 points 5. 10 points

Answer 54

0 points **Most people with Turner syndrome have average intelligence, and their full-scale IQ scores are usually within the normal range

Question 55

The total number of possible different codons that can occur in a human DNA is Select one: 1. 24 2. 34 3. 18 4. 64 5. 36

Answer 55

64 Some amino acids are encoded by more than one codon, inasmuch as there are 64 possible base triplets and only 20 amino acids. In fact, 61 of the 64 possible triplets specify particular amino acids and three triplets (called stop codons) designate the termination of translation. Thus, for most amino acids, there is more than one code word.

Question 56

For any particular trait, the pair of alleles of each parent separate and only one allele passes on from each parent to an offspring. Which of the following Mendelian principles refer to the above phenomenon? Select one: 1. Law of common fate 2. Law of uniformity 3. Law of independent assortment 4. Law of segregation 5. Law of closure

Answer 56

The second Mendelian law is called the principle of segregation. It states that for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parent's pair of alleles is inherited is a matter of pure chance. For example if there are two alleles both determining black colour in mother and two alleles with one determining white colour and one determining black colour in the father, then these two alleles segregate and only one of them could be passed on to the second generation. This was later proved to be true by studying chromosomes during cell division.

Question 57

A man suffers from an autosomal recessive disorder and has mild learning difficulties and special dietary requirements. Which of the following enzymes is affected as a result of the mutated gene? Select one: 1. Phenylalanine hydroxylase 2. Phenylalanine decarboxylase 3. Alcohol dehydrogenase 4. Hypoxanthine guanine phosphoribosyl hydroxylase 5. Hypoxanthine guanine phosphoribosyl transferase

Answer 57

Phenylalanine hydroxylase The diagnosis is phenylketonuria, which is an inborn metabolic disorder with autosomal recessive inheritance. It is a complex metabolic condition caused by mutations of the phenylalanine hydroxylase gene.

Question 58

A 45-year-old man is diagnosed with cognitive impairment. The family history suggests that individuals in the most recent generations of the family pedigree have developed a myriad of psychiatric disturbances at an earlier age and with greater severity than previous generations. Choose one correct diagnosis. Select one: 1. Fragile X syndrome 2. Huntington syndrome 3. Motor neuron disease. 4. Velocardiofacial syndrome 5. Frontotemporal dementia

Answer 58

Huntington syndrome Huntington's disease is inherited in an autosomal dominant manner with full penetrance and a prevalence rate of about 5 per 100,000. The gene responsible is an expanded and unstable CAG trinucleotide repeat on the short arm of chromosome 4 - 4p16.3. This results in translation of an extended glutamine sequence in huntingtin, the protein product of the gene. Huntingtin is expressed throughout the body. Its function is unclear.Though slightly unusual for a genetic disease; the onset is usually between 30 and 50 years of age. Most adult-onset HD cases have CAG expansions of 40-55 repeats, while greater expansions (and more than 70 repeats) are seen in childhood-onset HD. The phenomenon of anticipation, as described in the above scenario, is well demonstrated in Huntington's.

Question 59

What is the likelihood (in percentage) of a man acquiring Huntington's disease if his father has the illness and carries the mutant chromosome? Select one: 1. 33 2. 75 3. 50 4. 25 5.100

Answer 59

50% Huntington's disease is transmitted by an autosomal dominant inheritance pattern. If one parent is an affected carrier, the likelihood of transmission to any given child is 50%. The protein huntingtin is coded on the short arm of chromosome 4.

Question 60

Soon after gamete fusion and fertilization, nondisjunction of chromosomes takes place in an early mitotic cell division in chromosome 21. Which of the following chromosomal makeup will be seen in the foetus? Select one: 1. Triploidy 2. 21 monosomy 3. Euploidy 4. 21 trisomy mosaic 5. 21 trisomy

Answer 60

21 trisomy mosaic These aberrations result from the failure of chromosome or chromatids to separate ('non-disjunction') in meiosis, with one gamete receiving two copies of that chromosome and one another with no copies of the chromosome. This can produce (i) an extra chromosome, so resulting in a fetus that is 'trisomic' and has three instead of two copies of the chromosome; or (ii) no chromosome, so the fetus is 'monosomic' and has one instead of two copies of the chromosome. Non-disjunction can occur with autosomes or sex chromosomes. However, only individuals with trisomy 13, 18 and 21 survive to birth, and most children with trisomy 13 and trisomy 18 die in early childhood. Occasionally, non-disjunction can occur during mitosis immediately after two gametes have fused. This leads to the formation of two cell lineages with different chromosomal makeup. Non-disjunction occurs more often with the sex chromosome, and sometimes with chromosome 21, resulting in a 'mosaic' individual.

Question 61

Molecular genetic findings in psychiatric disorders are consistent with which of the following models? Select one: 1. Single genes of large effect 2. None of the listed 3. Single genes of small effect 4. Multiple genes of large effect 5. Multiple genes of small effect

Answer 61

Multiple genes of small effect Multiple genes - small effect model proposes that diseases such as schizophrenia result from the co-action of multiple (ranging in principle from a few to many thousand) common variants (`polymorphisms'), each of which has a small effect on illness susceptibility. When an individual inherits several, or many, susceptibility variants together, they have a sizable influence on disease risk. Hence the mutations or polymorphisms are not sufficient by themselves to cause disease, but they occur very commonly so they can interact in combinations and produce the disease. This model is more popular currently and forms the basis of association and linkage studies being carried out widely.

Question 62

Which of the following terms refers to the phenomenon by which one genetic alteration influences another genetic alteration eventually mitigating the effects of each other? Select one: 1. Imprinting 2. Transition 3. Crossing over 4. Epistasis 5. Synapsis

Answer 62

Epistasis Gene-gene interaction between different alleles of different genes is called epistasis. This can occur at the same step or different stages of the same biochemical pathway. At times, the effect of one change may mitigate or modify the other.

Question 63

Which of the following disorders is inherited via X-linked dominant inheritance? Select one: 1. Cerebellar vermis herniation with hydrocephalus 2. Brain tumours, epilepsy, learning disability and multiple renal cysts. 3. A 3 yr old girl with learning disability and stereotyped hand movements around midline of her body. 4. A 2 yr old boy with repeated respiratory infections, puppet like face, hypothyroid profile and poor cognitive development born to a mother of advanced maternal age. 5. Pseudohypertrophy of calf muscles with normal IQ.

Answer 63

A 3 yr old girl with learning disability and stereotyped hand movements around midline of her body. Rett's syndrome - X-linked dominant. X-linked dominant disorders are rare. Because females have higher gene frequency for X chromosomes compared to males, females have twice as much chance as males to inherit an X-linked disease-causing mutation. Male to male transmission of the disease-causing mutation is not seen. Vitamin D-resistant rickets is the best-known example. An atypical pervasive developmental disorder called Rett's syndrome is inherited in X-linked dominant fashion. It is characterised by a deceleration in head circumference, learning disability and stereotyped hand movements around the midline of her body.

Question 64

An autosomal recessive disorder shows Hardy-Weinberg equilibrium. It has an incidence of 1 in 4900. The frequency of carriers of the disease is Select one: 1. 1 in 30 2. 1 in 70 3. 1 in 35 4. 1 in 10 5. 1 in 40

Answer 64

1 in 35 According to Hardy-Weinberg principle, the carrier frequency is twice the square root of the frequency of a disease.

Question 65

In which of the following types of inheritance, 25% of children inherit the disease even when both parents are apparently healthy but share a similar genotype? Select one: 1. X linked recessive 2. Mitochondrial 3. Autosomal dominant 4. Autosomal recessive 5. X linked dominant

Answer 65

Autosomal recessive Autosomal recessive disorders are only manifest in the homozygous state and normally only affect individuals in one generation, usually in one sibship in a family. They affect both males and females equally. Offspring of parents who are heterozygous for the same autosomal recessive allele have a 1 in 4 chance of being homozygous for that allele. The less common an autosomal recessive allele, the greater the likelihood that the parents of a homozygote are consanguineous.

Question 66

In which of the following phases of the cell cycle does cell division occur? Select one: 1. G1 phase 2. G0 phase 3. G2 phase 4. S phase 5. M phase

Answer 66

M phase Each cell undergoes a natural cycle in terms of its replication and nucleic acid synthetic activity. The cell cycle consists of four separate phases: G1 phase, S phase, G2 phase and M phase. G1 stands for growth phase 1, S for synthetic phase, G2 for growth phase 2 and M phase for mitosis phase. Cells in the quiescent G0 phase of the cycle are stimulated by the growth factors (e.g. EGF, epithelial growth factor; PDGF, platelet-derived growth factor; IGF, insulin-like growth factor) and result in activation of transcription factors and lead to the initiation of DNA synthesis, followed by mitosis and cell division. Thus from G0 the cell moves on to G1 when the chromosomes are prepared for replication. This is followed by the synthetic (S) phase, when the 46 chromosomes are duplicated into chromatids, followed by another gap phase (G2), which eventually leads to mitosis.

Question 67

Which of the following values of the log of odds [LOD score] is commonly used as a threshold level of significance in linkage studies? Select one: 1. More than 2 2. More than 0.05 3. More than 3 4. Less than 0.05 5. More than 1

Answer 67

More than 3 To estimate the likelihood that two loci are truly linked with a specific recombination frequency, an LOD score is used. An LOD score greater than 3 is usually interpreted as statistical evidence of linkage (i.e., the numerator is 1,000 times greater than the denominator, indicating that linkage is 1,000 times more likely than nonlinkage). Conventionally an LOD score of -2 or less is taken as evidence that two loci are not linked (i.e., nonlinkage is 100 times more likely than linkage).

Question 68

Which of the following best describes the term genotype? Select one: 1. The genetic makeup of a family with a specific disorder 2. An unobservable marker of familial risk for a condition 3. The detectable characteristics of an individual organism 4. A numerical representation of all of the potential combinations of parental traits. 5. The sum total of all the genes that is inherited by an organism.

Answer 68

The sum total of all the genes that is inherited by an organism. The term genotype describes the actual set of genes carried by an organism. In 1909, the clarifying distinction between the concept of "genotype" and the "phenotype" was provided by the Danish botanist Wilhelm Johanssen. Gottesman and Shields described "endophenotypes" as internal phenotypes discoverable by a "biochemical test or microscopic examination."

Question 69

Neuregulin-1 was identified as a candidate gene for schizophrenia after typing 950 microsatellite markers in 110 Icelandic patients. Which of the following approach was used to complete the above? Select one: 1. Family studies 2. Sib pair analysis 3. Whole genome scan 4. Association studies 5. Twin studies

Answer 69

Whole genome scan Stefansson et al. found that neuregulin-1 is a candidate gene for schizophrenia after typing 950 microsatellite markers covering the whole genome in 110 Icelandic patients for whom they had reconstructed their genealogical relationships. This was done using whole genome scan, which is a type of linkage analysis, where markers placed at regular intervals covering the whole genome, are typed. It is tedious but often the first approach when no genetic information is available about a particular phenotype (Advanced glossary on genetic epidemiology.

Question 70

If both parents are carriers of an autosomal recessive illness, then the probability of inheritance in children is Select one: 1. 1 in 4 2. 1 in 2 3. 100% 4. 1 in 3 5. 0%

Answer 70

1 in 4 If both parents carry ONE autosomal recessive gene each (both are carriers), there is a 1 in 4 chance of the child developing the disease. If both parents carry TWO autosomal recessive genes each (both are diseased), there is a 100% chance of the child developing the disease.

Question 71

The most common feature of Prader-Willi syndrome is Select one: 1. Epilepsy 2. Repeated hand wringing 3. Large testicles 4. Short stature 5. Simian palmar crease

Answer 71

Short stature The features of Prader-Willi syndrome includes obesity, small hands and feet, microorchidism, cryptorchidism (hypogonadism), short stature, almond-shaped eyes, flat face, prominent forehead and bitemporal narrowing and orthopaedic problems such as congenital dislocation of hip, scoliosis etc are seen as the child develops.

Question 72

A 17-year-old boy's mother and paternal aunt both suffer from alcoholism. Compared to the general population, the risk of alcoholism in this boy is increased by a factor of Select one: 1. 8 times 2. 3 times 3. 2 times 4. 16 times 5. 4 times

Answer 72

4 times Family studies show that the relative risk is increased by about 4-6 times for alcoholism if there is a strong family history. The majority of adoption studies show that the risk of alcoholism in adopted children is strongly correlated with their biological parents rather than adoptive parents (3-4 times higher).

Question 73

A common method used to measure recombination fraction in a linkage study is Select one: 1. Delta score 2. Log of odds score 3. Predicted recombination frequency 4. Genetic distance 5. Observed recombination frequency

Answer 73

Log of odds score LOD or logarithm of odds score is a measure of the statistical strength of association used in a genetic linkage analysis. The value of the LOD score is the ratio between the probability of obtaining a result (of association) if the two loci are linked to the probability of obtaining the results if the two loci are not linked. Higher the score, more the likelihood of a true association.

Question 74

Which of the following is not true concerning Huntington's disease? Select one: 1. Age of onset is inversely related to disease severity 2. Disease chromosome inherited from the father is unstable 3. Trinucleotide repeat of 34-45 is seen in normal individuals 4. Characteristic protein deposits form nuclear inclusions 5. Maternal inheritance results in more severe and earlier onset disease

Answer 74

Maternal inheritance results in more severe and earlier onset disease Spermatogenesis induces more instability in HD

Question 75

When the same disease phenotype is caused by mutations in different loci, this is called Select one: 1. Homogeneity 2. Epistasis 3. Allelic heterogeneity 4. Locus heterogeneity 5. Pleiotropy

Answer 75

Locus heterogeneity Locus heterogeneity exists when the same disease phenotype can be caused by mutations in different loci. Locus heterogeneity becomes especially important when genetic testing is performed by testing for mutations at specific loci. For example, early-onset Alzheimer's could be caused by mutations in chromosome 1, 14 or 21.

Question 76

Which of the following condition results from a genetic abnormality in the locus coding progranulin? Select one: 1. Primary progressive aphasia 2. Alzheimer's disease 3.Tay Sach's disease 4. Prion disease 5. Parkinson's disease

Answer 76

Primary progressive aphasia Progranulin (PGRN) mutations cause frontotemporal lobar degeneration (FTLD). Encoded by a single gene on chromosome 17q21, the mutations cause a clinical phenotype that is similar to those with sporadic frontotemporal dementia - primary progressive aphasic type.

Question 77

Which type of genetic study uses cases and controls or families with internal controls? Select one: 1. Segregation studies 2. Family studies 3. Association studies 4. Linkage analysis 5. Twin studies

Answer 77

Association studies The simplest scenario of genetic association analysis is to study the genotype frequency of a polymorphism in a group of independent patients (cases) and a group of normal individuals (controls). They might be designed as simple case-control studies, or even better if they make use of family-based internal controls.

Question 78

Which of the following methods can be used to detect the presence of abnormal trinucleotide expansions? Select one: 1. Northern blotting 2. Karyotyping 3. Southern blotting 4. PCR 5. FISH

Answer 78

PCR reveal large segments of missing or extra genetic material (e.g., in Down syndrome, there are three copies of chromosome 21; a female with Turner syndrome only has one X chromosome instead of two). FISH uses a protein, called a probe, to "stick" to a known sequence of DNA (usually a known mutation). If that sequence is present in a patient's sample, the probe will bind to it and light up under a fluorescent microscope. FISH also can be used to detect chromosome rearrangements, marker chromosomes (extra pieces of unidentified chromosomal material), and duplications or deletions of large pieces of DNA PCR is commonly used in medical and biological research labs to copy segments of DNA (called DNA amplification) so that sufficient quantities are available for further testing (e.g., forensic, medical, research). Relatively simple PCR-based assays can be used to determine the presence of the trinucleotide expansions. The size of the PCR product can be evaluated by polyacrylamide gel electrophoresis. The product length is detected by use of a radiolabeled primer to generate a radiolabeled product, e.g. a radiolabeled (CAG)n or (CTG)n oligonucleotide

Question 79

Which of the following phenomena explain most of the epigenetic variations? Select one: 1. Mutations and polymorphism 2. Aneuploidy 3. DNA methylation and histone modification 4. Polymorphism and microdeletions 5. Splicing errors and methylation

Answer 79

DNA methylation and histone modification DNA methylation and histone modification explain most the of epigenetic variations discovered to date. Crow has argued for long that epigenetic defects explain most of the concordance seen in schizophrenia; according to Crow, the hemispheric laterality and language specialisation unique to human brains is the source of schizophrenic defect and it can be ascertained only through an epigenetic enquiry.

Question 80

A 24-year-old woman has a 32-year-old brother with schizophrenia. What is the risk (expressed as percentage) of her developing schizophrenia according to DSM criteria? Select one: 1. 13 2. 6 3. 10 4. 2 5. 16

Answer 80

10% The lifetime risk of schizophrenia in the sibling of a patient is 9-10%.

Question 81

A patient is referred with a diagnosis of schizophrenia. Chromosome analysis shows a 22q11 deletion confirming a diagnosis of Di George syndrome. Which of the following is NOT compatible with this diagnosis? Select one: 1. pharyngeal insufficiency 2. supra-valvular aortic stenosis 3. hypercalcaemia 4. fish mouth 5. severe learning difficulties

Answer 81

hypercalcaemia In velo-cardio-facial or DiGeorge syndrome, hypoparathyroidism leading to hypocalcemia (observed in 60% of patients) usually begins in the neonatal period, occasionally manifesting in the form of tetany or tonic convulsions.

Question 82

Choose the correctly paired techniques and genetic tools. Select one: 1. Plasmid - Flourescent in situ hybridisation 2. Flourescent probes - Polymerase chain reaction 3. Heat denaturation - DNA cloning 4. Oligonucleotide primers - Western blotting 5. Vectors - DNA cloning

Answer 82

Vectors - DNA cloning A cloning vector is a small piece of DNA into which a foreign DNA fragment can be inserted

Question 83

Which of the following statements about zygosity in twins is true? Select one: 1. Dizygotes share all except few genes 2. Monozygotes are formed from two sperms fertilizing one ovum 3. Dizygotes and monozygotes have same amount of environmental sharing 4. Monozygotes share more uterine environment than dizygotes 5. Anatomical similiarity is sufficient to establish zygosity

Answer 83

Monozygotes share more uterine environment than dizygotes Monozygotic (MZ, or "identical") twins are formed when an embryo is cleaved during early development. The result is two genetically identical embryos. Dizygotic (DZ, or "fraternal") twins are the result of the fertilization of two different ova by two different sperm cells. DZ twins are genetically the same as non-twin siblings, sharing only 50% of their genes. Approximately 70% of monozygotic twins are monochorionic while dizygotes almost always have separate chorions/amnions. Hence, monozygotes share more uterine environment than dizygotes.

Question 84

Which of the following phenomenon has the highest heritability? Select one: 1. IQ 2. Neuroticism 3. Extraversion 4. Bipolar disorder 5. Novelty seeking

Answer 84

Bipolar disorder Bipolar disorder has higher heritability than other listed traits (>80%)

Question 85

Which of the following describes the process by which introns are removed from freshly made RNA sequences? Select one: 1. Post translational modification 2. Exocytosis 3. Cytokinesis 4. Splicing 5. Synapsis

Answer 85

Splicing Transcripted RNA initially contains the 'junk' sequences - introns that do not code for polypeptides. This unprepared RNA is called heterogeneous nuclear RNA or hnRNA. This hnRNA then undergoes splicing aided by nucleosomes in the nucleus to remove non-coding sequences and results in messenger RNAs (mRNA).

Question 86

Mr X is a tall man with low IQ and behaviour problems. Identify the type of sex chromosome disorder? Select one: 1. Downs syndrome 2. XYY male 3. Klinefelter's syndrome 4. Turner's syndrome 5. Trisomy X

Answer 86

XYY XYY males have a karyotype of 47, XYY. This condition is seen in 1:1000 male births. Behavioural problems are commonly seen. IQ may be slightly lower than average. Studies on the population of men in maximum-security psychiatric hospitals in the 1960s seemed to show an excess of men with this karyotype as well as men with Klinefelter's syndrome.

Question 87

Which of the following is true with regard to the genetic risk of schizophrenia when moving from a closer relative to a distant relative? Select one: 1. Risk initially increases, then falls 2. Risk increases 3. Risk depends on the sex of the relative 4. Risk remains the same 5. Risk decreases

Answer 87

Risk decreases For both schizophrenia and bipolar disorder there is a very rapid, non-linear decrease of risk when moving from a genetically identical individual (i.e. monozygotic co-twin where the risk is 50-60%), to an individual who shares half the genes (e.g. sibling, parent, dizygotic co-twin where risk is around 10%)

Question 88

In premutant carriers of fragile X expansion, which of the following features may be seen? Select one: 1. psychotic episodes 2. increased risk for intention tremor and ataxia 3. no clinical features 4. mental retardation 5. macroorchidism

Answer 88

increased risk for intention tremor and ataxia Men who are not retarded but carry an increased number of CGG repeats in the FMR1 locus are called premutation carriers. Though premutant carriers were long thought to be free from clinical features, it is now known that they are at increased risk for developing intention tremor and ataxia especially after middle age. Likewise, women who are premutation carriers (55-200 CGG repeats) are at increased risk of premature ovarian failure and/or mild cognitive or behavioral abnormalities.

Question 89

The gene polymorphism involved in serotonin transporter variations is Select one: 1. 5q31 2. SL6CA4 3. XLMR 4. Xq 26-27 5. HGPRT

Answer 89

SL6CA4 The gene that encodes the serotonin transporter is called solute carrier family 6 (neurotransmitter transporter, serotonin), member 4 (SLC6A4). In humans, the gene is found on chromosome 17 on location 17q11.1-q12. The promoter region of the SLC6A4 gene contains a polymorphism with "short" and "long" repeats in a region: 5-HTT-linked polymorphic region (5-HTTLPR or SERTPR). Serotonin transporter polymorphisms are noted in the promoter region, which is a non-coding part of DNA (5HTTLPR - 5HT transporter linked promoter region). 5HTTLPR can be of a short variant or long variant; hence it is classed as a 'length polymorphism'. In those with the short variant, the serotonin transporter expression is low; the short variant is speculated to be associated with higher incidence of affective disorders, neuroticism, anxiety and PTSD. But the evidence is inconclusive as most studies are case-control design with significant heterogeneity.

Question 90

The function of the enzyme RNA polymerase is best described as Select one: 1. Synthesis of multiple copies of damaged RNA 2. Synthesis of DNA from RNA template 3. Synthesis of DNA from DNA template 4. Synthesis of RNA from DNA template 5. Synthesis of RNA from RNA template

Answer 90

Synthesis of RNA from DNA template RNA Polymerase is an enzyme that catalyzes the synthesis of RNA from ribonucleoside triphosphates in the presence of a DNA template.

Question 91

You are seeing a 55-year-old man in the outpatients' clinic. He has a history of gradual progressive memory loss, and his MMSE is 20 out of 30. The gene implicated for his condition codes for Select one: 1. Glutamate 2. Presenilin-1 3. Neuronal Sortilin related receptors (SORL1) 4. Dysbindin 5. Apolipoprotein -E4

Answer 91

Presenilin-1 The presenilin-1 gene located on chromosome 14 and mutations in this gene can cause early onset Alzheimer's disease. SORL1 directs trafficking of APP into recycling pathways; when SORL1 is underexpressed, APP is sorted into Aß- amyloid generating compartments. SORL1 is associated with late onset dementia, not the presenile type.

Question 92

In which of the following mutations does the mutant codon specify a stop signal? Select one: 1. Missense mutation 2. Silent mutation 3. Nonsense mutation 4. Inframe mutation 5. Frameshift mutation

Answer 92

Nonsense mutation A silent mutation causes no change in protein product - this is possible because a single amino acid is often coded by more than one triplet sequence. In a silent mutation, one triplet sequence is replaced by a different sequence but without changing amino acid product. In missense mutation, the new mutant codon specifies a different amino acid with variable effects on final protein product. For example, haemophilia, sickle cell anaemia. In non sense mutation, the new codon is UUA UGA or UAG, which signals 'stop' to the amino acid sequence resulting in a nonfunctional protein.

Question 93

The risk of unipolar depression in a first degree family member with bipolar disorder is given by Select one: 1. 6-7 times higher 2. 2-3 times higher 3. 4-5 times higher 4. 8-9 times higher 5. 10 times higher

Answer 93

2-3 times higher Lifetime risk rates of unipolar disorder in a member of the general population unrelated to anyone with affective disorders is 5-10%. In relatives of a bipolar proband, the risk, of the unipolar disorder is A. first degree relative 10-20% (relative risk = 2-3times); B. monozygotic co-twin 15-25% (relative risk = 3-5 times). Also, note that the relatives of bipolar patients have a risk of 20-30% for 'any affective disorder' in their lifetime. Note that the risk to offspring with both parents affected by bipolar disorder is 50-65% risk for bipolar and 50-75% risk for any affective disorder.

Question 94

A mutation in the shank3 gene is associated with which of the following features? Select one: 1. Parkinsonism 2. Autism 3. Bulimia 4. Alcohol dependence 5. Anorexia nervosa

Answer 94

SHANK3 SHANK3 or 'SH3 and multiple ankyrin repeat domains 3' is located at 22q13.3. 22q13.3 deletion syndrome (called Phelan-McDermid syndrome) reduces cell-to-cell communication between neurons caused by a lack of SHANK3 protein contributing to the developmental delay, intellectual disability, and absent or severely delayed speech. At least seven SHANK3 gene mutations have been found in people who have the features of autism or similar conditions known as autism spectrum disorders

Question 95

In the human DNA, codons code for a specific Select one: 1. Sugar 2. Protein 3. Phosphate 4. Nuclei acid 5. Amino acid

Answer 95

Amino acid The genetic code is the relation between the sequence of bases in DNA (or its RNA transcripts) and the sequence of amino acids in proteins. Three nucleotides (codon) encode an amino acid. Proteins are built from a basic set of 20 amino acids, coded by several combinations of the four bases.

Question 96

In a patient with macroorchidism, large ears, prominent jaw, a high-pitched voice, and mental retardation, which of the following trinucleotide repeats could be seen? Select one: 1. CCT 2. CTG 3. CGG 4. CTT 5. CAG

Answer 96

CGG The above description suits Fragile X syndrome. This X-linked condition accounts for more cases of mental retardation in males than any other condition except Down syndrome with a frequency of 1 in 4000. It can affect females but 50% less frequently than in males. A fragile site near the tip of the long arm of the X chromosome was initially suspected. Now it is known that fragile X results from an expansion of a trinucleotide repeat (CGG) near a gene called FMR1.

Question 97

The origin of single X chromosome in Turner's syndrome is most likely to be of Select one: 1. Dizygotic twin origin 2. None of the listed 3. Paternal origin 4. Chromosome escaping random inactivation 5. Maternal origin

Answer 97

Maternal origin As nearly 80% of meiotic error in Turner's is paternal, the remaining single X chromosome is usually of maternal origin.

Question 98

Which of the following inheritance patterns includes maternal transmission but no paternal transmission and affects both sexes? Select one: 1. Mitochondrial 2. Autosomal dominant 3. X liked dominant 4. Genomic imprinting 5. X linked recessive

Answer 98

Mitochondrial Mitochondrial DNA is wholly inherited from the ovum. The sperm has no mitochondria in its head; the head is made of nuclear material and acrosomal cap. The body of sperm has many mitochondria that provide energy in propelling the tail. The body and tail are shed on the entry of sperm into the ovum. Hence, the mitochondria of an embryo are completely maternal-derived.

Question 99

Right homonymous hemianopia is caused by which of the following lesions? Select one: 1. Optic chiasma lesion 2. Lesions of right optic radiation 3. Lesions of left optic radiation 4. Lesions of right optic nerve 5. Lesions of left optic nerve

Answer 99

Lesions of left optic radiation Lesions of the left-sided optic tract, lateral geniculate body, optic radiations, and striate cortex (any retro chiasmatic structure) can cause right homonymous hemianopia.

Question 100

The number of daughter cells at the end of a complete meiosis of one human cell is Select one: 1. 2 2. 5 3. 4 4. 3 5. 1

Answer 100

4 Meiosis is divided into two parts: meiosis I and meiosis II. At the end of the meiotic divisions, there are four daughter cells whereas only two are produced from the mitotic process. Of the two parts of meiosis, meiosis 1 is the reduction division. The main differences from mitosis are the occurrence of synapsis (crossing over) in the prolonged prophase phase and non-separation of sister chromatids during anaphase 1, leading to reduced (half) chromosomal numbers in daughter cells. Meiosis 2 is same as a normal mitosis (no reduction in chromosomal numbers).

Question 101

In a family with the X-linked recessive transmission of a genetic disease, there are two daughters and one son born to a diseased father and normal non-carrier mother. One of the two daughters exhibits a moderate degree of the disorder while the other is a silent carrier. Which of the following can explain the above? Select one: 1. The daughter is biologically male 2. Combined X linked dominant and recessive transmission 3. Diseased daughter is the unaffected carrier 4. The disease cannot be X linked recessive 5. Unfavourable lyonisation of X chromosomes

Answer 101

Unfavourable lyonisation of X chromosomes If a recessive disease-causing mutation occurs on the single X chromosome of a man, this is sufficient to cause disease as another X chromosome is not available to compensate any deficiencies. As females have two copies of the X chromosome, they need a double identical mutation for disease expression which is extremely rare. But during random X inactivation if most X chromosomes carrying normal alleles are inactivated (called unfavourable Lyonisation), then these females can manifest the disease phenotype "termed as manifesting heterozygotes. But nevertheless the severity of expressed disease is mild and can go unnoticed too.

Question 102

Which of the following best describes the commonest type of mutations seen in thalassemia? Select one: 1. Nonsense 2. Inframe 3. Missense 4. Frame shift 5. Silent

Answer 102

Missense Beta thalassemia is the commonest single gene disorder in the world. It is generally considered as an autosomal recessive disorder as the inheritance of two mutant ß-globin genes is necessary to produce a notable clinical illness. It is characterized by mostly missense or somewhat less frequently nonsense mutations in the [beta]-globin gene (HBB), which reduce or completely abolish gene expression. Heterozygous inheritance of a [beta]-thalassemia mutation results in a trait condition, sometimes termed [beta]-thalassemia minor. Homozygous inheritance results in [beta]-thalassemia major (absent Hb A production) or [beta]-thalassemia intermedia (severely reduced Hb A production), which are associated with moderate to severe hemolytic anemia.

Question 103

Which of the following is NOT a step in polymerase chain reactions? Select one: 1. Cycling 2. Annealing the DNA 3. Extending the primers 4. Gel electrophoresis 5. Denaturing the DNA

Answer 103

Gel electrophoresis Minute amounts of DNA can be amplified over a million times using an in vitro technique called polymerase chain reaction. The technique has three steps. Double-stranded genomic DNA is denatured by heat into single-stranded DNA. The reaction is then cooled to favour DNA annealing, and the primers bind to their target DNA. DNA polymerase is used to extend the primers in opposite directions using the target DNA as a template. After one cycle, there are two copies of double-stranded DNA, after two cycles there are four copies, and this number rises exponentially with the number of cycles. The cycling is set to produce necessary number of amplifications. Gel electrophoresis is not an inherent part of PCR.

Question 104

Following synthesis, proteins inside the cell are stored temporarily in Select one: 1. Ribosomes 2. Nucleus 3. Nucleolus 4. Golgi complex 5. Cilia

Answer 104

Golgi complex The Golgi complex is a dynamic system that gives off vesicles and vacuoles for further processing and transport of synthesized protein molecules.

Question 105

Heritability is a measure of Select one: 1. Concordance of disease between twins 2. Risk of disease in first degree relatives of probands 3. Genetic contribution of disease in an individual 4. Degree of penetrance of a disease 5. Genetic contribution to phenotypic variation in population

Answer 105

Genetic contribution to phenotypic variation in population The relative influence of genetic factors in determining the variance in a trait is expressed as heritability.

Question 106

Choose the correct statement concerning Prader-Willi syndrome Select one: 1. Associated with short stature 2. Occurs only in males 3. Social anxiety is a common feature 4. Affected children have a normal IQ 5. Average life expectancy of 6 to 8 years

Answer 106

Associated with short stature Patients with PWS are often short statured and obese with learning disabilities.

Question 107

Which of the following blotting techniques can be used to visualize restriction fragment length polymorphisms? Select one: 1. Southern blot 2. Northern blot 3. Dot blot 4 .Eastern blot 5. Western blot

Answer 107

Southern blot Restriction fragment length polymorphisms are those variations which change the sites at which restriction enzymes can act on a DNA molecule, rendering differences in the final 'restricted' or cleaved DNA when these enzymes are applied in vitro. These fragments can be visualized on a Southern blot

Question 108

In Robertsonian translocation, the fusion usually occurs at the Select one: 1. Cytoplasm 2. Centromere 3. Non sense mutations 4. Stop codons 5. Aneuploidy

Answer 108

Centromere A Robertsonian translocation is a type of nonreciprocal translocation involving two homologous (paired chromosomes) or non-homologous chromosomes (i.e.,. two different chromosomes, not belonging to a homologous pair). A feature of chromosomes that are commonly found to undergo such translocations is that they possess an acrocentric centromere (having a large arm with the majority of genes, and a short arm with sparse number of genes). During a Robertsonian translocation, chromosomes break at their centromeres and the two long arms fuse to form a metacentric chromosome. The short arms also join to form a smaller chromosome, but this small piece gets lost over a few cell divisions.

Question 109

Which of the following is least likely regarding diseases that show the phenomenon of anticipation? Select one: 1. Dominant mode of transmission is noted 2. The age of onset and severity of illness reduces with successive generations 3. Trinucleotide expansion is seen 4. Infants are normal at birth 5. Most of them are neuro-degenerative disorders

Answer 109

The age of onset and severity of illness reduces with successive generations With successive generations, if the onset is earlier and the outcome becomes more severe in a genetic disease, the term anticipation is employed to describe the inheritance.

Question 110

Which of the following refers to the production of new copies of RNA from DNA? Select one: 1. Translation 2. Synapsis 3 .Replication 4 .Transcription 5. Modification

Answer 110

Transcription Using DNA template to form more DNA is replication; Using DNA template to form more RNA is transcription; Using RNA template to form protein is translation.

Question 111

If a disease has 75% heritability, then which of the following statement is correct? Select one: 1. 75% of the diseased patients have inherited the condition 2. 75% of the disease related genes are passed on from one generation to another 3. The risk of the disease in first degree relatives of patients is 75% 4. 75% of the features seen in a diseased patient is due to genetic component 5. 75% of the liability for the disease is inherited

Answer 111

75% of the liability for the disease is inherited Heritability is defined by the proportion of variation of an observed feature that is due to genetic factors.

Question 112

A 77-year-old Vietnam War veteran presents with shooting pain in his back. On neurological examination, you find light near dissociation of Argyll Robertson Pupil. Which of the following is true? Select one: 1. Consensual light reflex will be present 2. Both light and accommodation reflex will be present 3. Light reflex will be present 4. Accommodation reflex will be present 5. Afferent pupillary defect will be seen

Answer 112

Accommodation reflex will be present ARP - Argyll Robertson Pupil (note: Accommodation Reflex Present -light reflex absent) is due to an afferent defect in the pupillary reflex pathway - most probably a pretectal lesion.

Question 113

Which of the following enzymes mediate the binding of tRNA with amino acids? Select one: 1. RNA polymerase 2. Protein synthetase 3. Amino acid dehydrogenase 4. Aminoacyl synthetase 5. Reverse transcriptase

Answer 113

Aminoacyl synthetase While syntheszing protein chains, the correct amino acid is added to the coding tRNA by a specific enzyme called aminoacyl-tRNA synthetase. This synthetic process is called aminoacylation.