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Genetics MCQ Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

After genome-wide linkage analysis to map a disease locus we obtained a max LOD SCORE of 2 at theta 0 for a specific marker. What is the probability of linkage (marker-disease locus) vs no linkage?

A

100:1

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2
Q

In a given population the frequency of males affected by hemophilia is 1/100. If the population is in Hardy Weinberg equilibrium, what is the probability of having affected females?

A

(1/100)^2 = 1/1000

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3
Q

Relevant numbers about the human haploid genome, number of chromosomes, number of genes…?

A

3 billion base pairs, 46 chromosomes, 25000 genes

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4
Q

What is a backcross?

A

Is a type of breeding experiment used in genetics where an offspring is crossed with one of its parents or and individual genetically similar. It is done to isolate a desired trait, study inheritance patterns.

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5
Q

What were the main goals of the human genome project?

A
  1. Determine the DNA sequence of human genome and put it in some public database.
  2. Develop new technologies to make sequencing process more efficient.
  3. Identify DNA variations.
  4. Interpret the function of DNA on a genomic scale.
  5. Compare human DNA with DNA of lab animals.
  6. Reading human DNA in order to prevent the onset of diseases
  7. Apply new bioinformatics tools.
  8. Create a new generation of scientists.
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6
Q

Define the key features of a molecular marker…?

A

Markers present in the DNA sequence, easy to detect via PCR, lots of polymorphisms (common >1%), codominant in nature.

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7
Q

Explain the concept of incomplete dominance..?

A

A type of inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in
combined phenotype. When both alleles of a gene are expressed, give rise to a new blended phenotype.

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8
Q

What is the likely consequences of a nonsense mutation in the last exon of a gene?

A

The premature stop codon will be considered physiological and translation will halt, leading to a truncated protein.

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9
Q

What is the probability for a carrier couple to have 2 consecutive affected offspring?

A

1/16

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10
Q

What do we mean with F1 generation? What are the expected genotypes?

A

First filial generation. Gametes from parents. Genotype Aa

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11
Q

What do we mean with F2 generation? What are the expected genotypes?

A

Second filial generation. Crossing F1 individuals, obtaining 3:1 ratio (dominant: recessive), AA, Aa, aa.

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12
Q

How many cells in a Punnett square for trihybrid crosses?

A

2^3 = 8, 8x8=64

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13
Q

What are the mechanisms through which loss of a function mutation can be dominant?

A

Through haploinsufficiency (when one wt copy of the gene isn’t enough to yield sufficient product) & dominant negative affect (altered gene product acts antagonistically to that of the wt allele), gain of toxic function.

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14
Q

What is the probability for a carrier couple to have 2 consecutive affected SONS ?

A

1/64

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15
Q

What are the typical effects of mutations in tumor suppressor and oncogenes?

A

In oncogenes, leads to gain of function (uncontrolled cell growth), in tumor suppressor leads to loss of function (no apoptosis/inhibition of cell growth), favors tumor growth

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16
Q

What is linkage disequilibrium?

A

Refers to the non-random association of alleles at different loci. It occurs when the combination of alleles or genetic markers in a population is different from what would be expected if the loci were independently assorting according to Mendelian genetics.

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17
Q

What odd ratio indicates in populational risk?

A

Probability of having the disease in respect to the population.

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18
Q

What is the effect of transplantation of paternal haploid pronucleus into a haploid androgenic cell?

A

UPD (uniparental disomy)

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19
Q

What are the 5 conditions of HW equilibrium?

A

Big population, random mating, absence of migratory flux, no new mutations and selective pressure on genotype

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20
Q

What is whole exome sequencing?

A

When technology is used to sequence only the exons of the genome with the aid of primers that identify exons via hybridization to them.

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21
Q

What is genomic imprinting?

A

It is the different expression of paternal and maternal copies of some gene.

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22
Q

What are homeobox genes?

A

Master regulators of development. A family of genes that determine the formation of body parts during embryonic development.

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23
Q

What is heterochromatin?

A

Very close areas of the chromosomes that are not supposed to be transcribed so these areas are inaccessible to RNA polymerase.

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24
Q

What are the peculiar features of HD?

A

Anticipation, autosomal dominant, fully penetrant, dynamic mutation disease.

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25
Q

How can CGH resolution be increased?

A

Through the use of microarrays in conjuction with CGH technology. The more specific of array CGH has been developed allowing for a
locus-by-locus measure of CNV with increased resolution as low as 100 kb

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26
Q

What is the average size of chromosomal band?

A

10 Mb

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27
Q

What is loss of heterozygosity?

A

Loss of one allele at a specific locus, caused by deletion mutation or loss of one chromosome from a pair, resulting in abnormal hemizygosity.

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28
Q

Describe the experiment of Mary Lyon?

A

Experiment with RBC culture demonstrated that the Barr body formation occurred randomly in cells.

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29
Q

When do Prader Willi Syndrome appear as fully penentrant?

A

When it’s inherited from the father.

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30
Q

Splicing mutation to skip on exon always associated with frameshift, why?

A

Nutation in the splice site allows for one/more introns to remain in the mature RNA, changing the number of nucleotides. It’s like an sinertion, leading to production of abnormal proteins

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31
Q

What molecular cause Bombay?

A

Homozygous recessive (hh) gene that impedes production of A/B proteins, causing AB blood types to test as 0.

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32
Q

Definition of SNP?

A

Variation of a single nucleotide base in DNA sequence, commonly
occurs in the population, is not pathogenic.

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33
Q

Do X and Y recombine? How?

A

They recombine ar the pseudoautosomal region. They recombine during pairing in meiosis I, crossing over, segregation.

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34
Q

Definition of an allele?

A

Alternative forms of genes that rise by mutation and are found at the
same place on a chromosome.

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35
Q

Four different species for genetics studies:..?

A

Drosophila, yeast, mouse, c. elegans

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36
Q

Ratio of yellow peas in F2 in dihybrid crosses:..?

A

(9+3/16) = ¾

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37
Q

Definition of monohybrid:..?

A

Breeding experiment between P generation (parental) organisms that differ in one trait.

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38
Q

Characteristic of mendelian pea’s:..?

A

Clear phenotypes, pure breeding lines, not linked, inheritance is not blended.

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39
Q

What is a reciprocal and unbalanced translocation?

A

When non-homologous chromosomes break and exchange fragments (eg. Philadelphia translocation).

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40
Q

Why can we define the genetic code as degenerative?

A

Because there are 64 possible triplets coding for 20 aa. Redundancy, more than one codon can code for the same aa.

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41
Q

What is haploinsufficiency?

A

Diploid organism has a single functional copy, 50% of gene
product is not enough to keep the wt phenotype, so it gives rise to the disease. One wt gene product is not sufficient to produce enough product.

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42
Q

What is genome wide linkage analysis?

A

A statistical way to work out the distance between two markers in human pedigrees on the base of recombination.

43
Q

What is LOD SCORE?

A

Probability to see recombination if loci are linked. It is used in linkage analysis.

44
Q

Diabetes has a relative risk for siblings=15. What does this mean?

A

Siblings of an affected individual have 15 times higher probability to develop the disease compared to a random individual in the population.

45
Q

What is a two-hit mechanism (as retinoblastoma)? What are its consequences for the disease way of inheritance?

A

First hit—> individual inherit the defective RB1 allele in every cell of their body due to their family.
Second hit—> aka somatic mutation, for retinoblastoma to develop the second allele must be inactivated or lost in a single cell.

46
Q

What is a barr body?

A

Inactivated X chr which is hyper condensed so it’s not accessible to
RNA polymerase.

47
Q

How many proteins are encoded by the mitochondrial genome?

A

13

48
Q

What are maternal effect genes?

A

Where the phenotype is completely derived from the genotype of the mother.

49
Q

What is the function of topoisomerase II?

A

Enzymes that disentangle the topological problems that arise in double-stranded DNA.

50
Q

What is negative dominance? If possible prove an example

A

Negative dominance refers to a genetic phenomenon where the presence of a particular allele in the heterozygous state results in a phenotype that is either less favorable or more deleterious than either the homozygous dominant or homozygous recessive states. Osteogenesis imperfecta.

51
Q

What is SRY?

A

Sex reversal on the Y-chr. If this transcription factor is present the testes develop in the embryo. These secrete testosterone which causes the development of the male phenotype.

52
Q

What are type I and II dynamic mutations?

A

A type-1 dynamic mutation is the expansion of a sequence in an exon, which causes a dominant gain-of-function mutation, ex. Huntington’s Disease.

A type-2 dynamic mutation is the expansion of a sequence in a noncoding sequence which can either be 5’ UTR , 3’ UTR or an intron. Type-2 dynamic mutations are loss-of-function mutations, they can both be recessive or dominant. Ex. Fragile X syndrome.

53
Q

What type of damage causes UV radiation?

A

Thymine dimers

54
Q

What type of repair comprehends the enzyme Glycosylase?

A

Base excision repair

55
Q

It has been noted a missense mutation in factor VIII, Leu to Ile, in an individual affected by
hemophilia. If in another female has been found the same mutation in factor VIII it is possible
to say that the mutation is always pathogenic?

A

Wrong

56
Q

What causes a PTC in the last exon of a gene?

A

Production of a truncated protein

57
Q

ATM gene with the mutations, Which type of mutations are them?

A

Loss of Function

58
Q

APOL1 what is the false statement?

A

The risk factor associated with chronic kidney disease is
dominant

59
Q

De novo mutation with the two parents which are healthy can be considered?

A

Strong
Pathogenic

60
Q

The probability of a male of being affected by hemophilia is 1/100, What is the probability of a
female of being affected?

A

0.0001

61
Q

Hemophilia A and Hemophilia B have a similar phenotype, but they’re caused by a mutation in
different genes on the x chromosome, what type of phenomenon is it?

A

Locus heterogeneity

62
Q

What is the resolution of metaphase FISH?

A

1-5 Mb (several Mb in the notes)

63
Q

Which of these type of proteins are not protoncogene?

A

DNA mismatch repair

64
Q

Which of these statements is false regarding the tumor cloning theory?

A

Tumor cells have 46
chromosomes

65
Q

Diabetes have relative risk for siblings (lambda) of 15, what does it means?

A

It means that the siblings of an affected individual have 15 times more chance to develop the disease with respect to the

66
Q

Which of the following alternatives is false regarding mosaicism?

A

A mutation during
gametogenesis is a cause of mosaicism

67
Q

After genome-wide linkage analysis to map a disease locus we obtained a max LOD SCORE
of 3 at Recombination fraction 0 for a specific marker. What is the probability of linkage
(marker-disease locus) vs no linkage?

A

1000:1

68
Q

What are the conditions for the Hardy-Weinberg equilibrium?

A

Large population, Random
Mating, Absence of new mutations, Absence of selective pressure, Absence of migration

69
Q

What are the possible causes behind an association between a SNP associated with a risk
factor and a disease?

A

Direct causation : the SNP is the risk factor itself causing the disease.
Linkage disequilibrium: the SNP is not directly causative but it is in linkage disequilibrium with another genetic variant that is the actual cause.
Population stratification
Pleiotropy

70
Q

What type of mouse model would you do in case of a disease cause by either a nonsense or frameshift mutation?

A

Can do a Knock-out mouse for the gene of interest using CRISPR/Cas9 to knock out a specific gene.

71
Q

Which of the following sentences is false regarding x-linked recessive diseases?

A

All women
are asymptomatic

72
Q

In a case control study the ratio of major/minor allele in case is 0.8/0.2 while in control 0.7/0.3.
What can you infer from these data?

A

The probability of having the disease in people carrying
the major allele is 70% higher than the general population

73
Q

Which meiosis are informative?

A

None of them

74
Q

Definition of overdominance (If possible provide an example)?

A

Also known as heterozygote advantage, occurs when the heterozygote genotype has a higher fitness than either the homozygote genotypes. This leads to the maintence of genetic variation in the population. An example is the genetic context of sickle cell anemia.

75
Q

Definition of linkage disequilibrium.

A

It occurs when alleles at different loci are inherited together more (or less) often than expected by chance. It indicates a non-random association between genetic variants within a population.

76
Q

How could you investigate possible pathogenic effects of a newly identified missense variant?

A

Bioinformatics analysis, conservation analysis, functional studies, segregation analysis, population analysis.

77
Q

The(result(of(Mutually(exclusive(events(is…( (

A

the(sum(

78
Q

What is the central dogma?

A

DNA is transcribed to RNA then translated to proteins.

79
Q

Bayes with given recombination fraction?

A

Affects prior

80
Q

Examples of GOF in proto oncogenes

A

Once mutated they become concogenes. Retinoblastoma

81
Q

In haplotype analysis what is the phase?

A

Describes the allergic combination of 2 homogous chromosomes

82
Q

What is a transversion?

A

Change between a purine and pyrimidine

83
Q

Can a silent mutation be pathogenic?

A

Yes they can occur although rare. They can cause altered rna stability, translation efficiency and even cause problems during protein folding.

84
Q

What is epistasis?

A

The effect of one gene masks the effect of another

85
Q

What is pleiotropy?

A

The effect of one gene is modulating the effects of many other genes.

86
Q

Potential mechanism for inactivation of Rb allele in retinoblastoma tumor arising in one of patients include:

A

a. Mitotic crossing over
b. Independent point mutation
c. All the answers are correct
d. Loss of chromosome 13

87
Q

Comparing SNPs and microsatellites, which answer is correct?

A

b. Microsatellites have more alleles than SNPS

88
Q

Functional studies shown the deleterious effects of a newly identified variant that co-segregates with the disease. In terms of pathogenicity it constitutes:

A

c. strong evidence of pathogenicity

89
Q

Splicing-affecting mutations, select the false answer:

A

d. splicing mutation that leads to skipping of one exon is always associated with frameshift.

90
Q

When a mendelian disease is said to be heterogenous?

A

Two or more genes act independently to cause an ideal trait

91
Q

Which statement is false about NMDdecay?

A

UPF proteins connect the stalled ribosome to adjacent EJC.

92
Q

Which is a strong evidence of the genetic component that causes type 1 diabetes mellitus?

A

The concordance rate in monozygotic twins is 5 times higher than dizygotic twins

93
Q

Which is not a typical mechanism by which a proto-oncogene is converted into an oncogene?

A

Complete deletion

94
Q

Choose the incorrect option about penetrance:

A

If penetrance is 100% the expressivity is 100%

95
Q

With reference to DNA repair, which of the following statements, if any, is false?

A

Most of the time DNA repair involves a mechanism that makes a repair to both DNA strands.

96
Q

A mutation of DNA within simple somatic cells in a multicellular organism:

A

May have phenotypic consequences

97
Q

What(is(the(size(of(the(mitochondrial(genome?(

A

16000 base pares, 37 genes encoding for 2 rrna

98
Q

What is a nonsense mutation?

A

Point mutation that introduces premature stop codon

99
Q

What is heteroplasmy?

A

The presence of of more that one type of organellae genome,

100
Q

What is the difference between Mendel’s first and second law?

A
  1. The first law aka law of segregation states that during the formation of gametes, two alleles for a gene segregate so that each gamete only carries one for each gene.
  2. The second law aka law of independent assortment states that the alleles for different traits are distributed independently of one another into gametes.
101
Q

Define reverse mutation.

A

Reversion of a mutant gene to the original phenotype (through a further mutation).

102
Q

What techniques are used in screening for mutation?

A

ARMS); Commercial formats (ex. Taqman Assay).

103
Q

What is mesonephros?

A

Gives rise to the definitive kidney

104
Q

SCP (Single Strand Conformation Polymorphism)

A

A single nucleotide change in a particular sequence cannot be distinguished by electrophoresis.

Medical Genetics (2 decks)

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