Genetics

Question 1

19755 – During the replication of DNA
A. introns are spliced out of the DNA molecule
B. mutations arising in a non-coding region are clinically unimportant
C. deletion of a whole gene will always be detectable by karyotype analysis
D. point mutations may result in an abnormally short protein chain
E. RNA polymerase is important in the replication process

Answer 1

D
Robbins 5th ed. Pages: 153; 126 Selected Topics D3-D5

Question 2

9750 – Aneuploidy
1: may be detected by karyotyping
2: is characterised by the formation of a ring chromosome
3: rarely arises during the first meiotic division
4: in tumour cells may be detected by flow cytometry

Answer 2

TFFT
Robbins, 6th ed, Ch 6

Question 3

12949 – Aneuploidy describes the chromosomal abnormality in
1: most patients with Down’s syndrome
2: all trisomy syndrome
3: Turner’s syndrome
4: poly-X females

Answer 3

TTTT
Aneuploidy refers to a chromosome number different from the normal or euploid number. Aneuploid cells may have more or fewer chromosomes than normal. In man normal diploid cells have 46 chromosomes. Most patients with Down’s syndrome have trisomy of chromosome 21 (A true). Turner’s syndrome occurs in females who have a single X chromosome (XO) instead of the normal XX (C true). X chromosomes in excess of normal are compatible with life, and are found in poly-X females (D true).

Question 4

21758 – Down’s syndrome due to trisomy 21
1: is most commonly caused by meiotic nondysjunction
2: is associated with an increased incidence of childhood leukaemia
3: is the commonest form of autosomal trisomy
4: in milder cases may be associated with mosaicism

Answer 4

TTTT
Robbins 6th ed. Pages: 170-1

Question 5

22444 – In Turner’s syndrome
1: the individual may show mosaicism with respect to the sex chromosomes
2: the condition is unlikely to be due to nondysjunction
3: the condition is not likely to be due to a balanced reciprocal translocation
4: most fetuses survive to birth

Answer 5

TFTF
Robbins 5th ed. Pages: 160-161; 152

Question 6

10336 – What type of underlying genetic abnormality is most commonly seen with Angelman syndrome
A. Point mutations
B. Gonadal mosaicism
C. Genomic imprinting
D. Deletions
E. Triplet repeat mutations

Answer 6

C

Question 7

18820 – The most usual chromosome complement in Klinefelter’s syndrome is
A. 44 autosomes plus XXY
B. 44 autosomes plus XY
C. 45 autosomes plus XXY
D. 44 autosomes plus XO
E. 43 autosomes plus XXY

Answer 7

A
Robbins 5th ed. Page: 159

Question 8

10330 – What type of underlying genetic abnormality is most commonly seen with cystic fibrosis
A. Point mutations
B. Gonadal mosaicism
C. Genomic imprinting
D. Deletions
E. Triplet repeat mutations

Answer 8

D

Question 9

10324 – What type of underlying genetic abnormality is most commonly seen with osteogenesis imperfecta
A. Point mutations
B. Gonadal mosaicism
C. Genomic imprinting
D. Deletions
E. Triplet repeat mutations

Answer 9

B

Question 10

10342 – What type of underlying genetic abnormality is most commonly seen with beta-thalassaemia
A. Point mutations
B. Gonadal mosaicism
C. Genomic imprinting
D. Deletions
E. Triplet repeat mutations

Answer 10

A

Question 11

23969 – In an individual with sickle cell trait (heterozygote)
1: an abnormal haemoglobin is synthesized
2: the haemoglobin precipitates at high oxygen concentrations
3: there is only mild likelihood of vascular occlusions
4: haemolytic crises are a prominent feature

Answer 11

TFTF
Robbins 5th ed. Chapter: 13 Pages: NOT GIVE

Question 12

10356 – What type of underlying genetic abnormality is most commonly seen with Fragile x syndrome
A. Point mutations
B. Gonadal mosaicism
C. Genomic imprinting
D. Deletions
E. Triplet repeat mutations

Answer 12

E

Question 13

9025 – The relevant gene is on the X chromosome in
1: familial polyposis coli
2: glucose 6-phosphate dehydrogenase deficiency
3: haemophilia B
4: haemophilia A

Answer 13

FTTT
Robbins, 6th ed, Ch 6

Question 14

23684 – Concerning familial hypercholesterolaemia
1: there is a mutation in the gene for high-density lipoprotein receptor
2: it is inherited as an autosomal dominant condition
3: the relevant gene is on chromosome 19
4: almost all cases have been shown to have the same mutation

Answer 14

FTTF
Robbins 6th ed. Pages: 145, 150-153.

Question 15

23569 – In disorders with multifactorial inheritance
1: mutations may be present in more than one gene
2: the risk of recurrence in subsequent pregnancies is less than 10%
3: identical twins will show 100% concordance
4: the severity of expression is constant for a given condition

Answer 15

TTFF
Robbins 4th ed. Pages: 154-155

Question 16

10368 – The following characteristics suggest that the disease is inherited as a multifactorial trait:
1: The disease occurs more frequently in the children of an affected person than among the grandchildren.
2: The incidence of the disease in the population is 3% and is 50% in the offspring of the affected person.
3: The risk of developing the disease is greater if both parents are affected than if only one parent is affected.
4: The disease occurs more frequently in women than in men.

Answer 16

TFTT

Question 17

22439 – Diseases inherited as autosomal recessive include
1: cystic fibrosis
2: achondroplasia
3: sickle cell anaemia
4: congenital agammaglobulinaemia

Answer 17

TFTF
Robbins 6th ed. Pages: 145
2: AD
4: X-linked recessive

Question 18

24024 – In disorders inherited by autosomal recessive inheritance
1: enzyme proteins are often affected
2: heterozygotes produce insignificant amounts of normal enzyme
3: complete penetrance is rare
4: onset is often early in life

Answer 18

TFFT
Robbins 5th ed. Pages: 129

Question 19

12964 – In diseases with an autosomal recessive inheritance, typically,
1: all children of an affected parent will be carriers
2: the parents of an affected individual usually appear normal
3: the birth of an affected child is usually the first indication of the disease in a family
4: both of the parents have transmitted the disease

Answer 19

TTTT
Recessive genes manifest their presence in the homozygous state, ie the relevant gene is present in double dose. Homozygous patients will have received one copy of the gene from each of their parents (D true), who are typically asymptomatic carriers (B true). They are usually unaware of their carrier state until they have produced an affected child (C true). All children of an affected parent will receive the relevant gene (since he/she is homozygous), and will typically be carriers (A true), though the parent’s children could manifest the disease if the parent’s partner also carried the relevant gene.
This would not, however, be typical.

Question 20

23294 – In a disease showing autosomal dominant inheritance
1: very few cases are due to de novo mutations
2: the mutations usually involve enzyme proteins
3: the disease is not necessarily clinically apparent at birth
4: approximately half of the patient’s children are likely to manifest the disease

Answer 20

FFTT
Robbins 6th ed. Page: 144-145

Question 21

23759 – Single gene disorders with an autosomal dominant pattern of inheritance
1: usually arise as new mutations
2: almost always present in early childhood
3: commonly involve the genes for enzymes
4: characteristically show variable expressivity

Answer 21

FFFT
Robbins 5th ed. Page: 128-129

Question 22

16974 – S: The effects of carcinogenic initiators on DNA chemistry are reversible because R: tumours do not eventuate if the subsequent promoter application is delayed.

Answer 22

Both S and R are false
This is central to the ‘initiator’ and ‘promoter’ model. Initiation is rapid, irreversible and has ‘memory’: ie application of the promoter by appropriate method and amount is equally effective whether it follows application of the initiator immediately, or after a delay. The action of the promoter is, however, potentially reversible as shown by the fact that divided doses of promoter cannot be separated by too long an interval, or the promoter effect is lost: ie some form of repair has occurred
between applications of the promoter.

Question 23

24074 – Regarding single-gene (Mendelian) disorder
1: X-linked disorders are the most common type
2: mutations in structural genes are commonly transmitted as autosomal dominant
3: most X-linked disorders are codominant
4: familial hypercholesterolaemia is caused by a mutation in the gene for a membrane receptor

Answer 23

FTFT
Robbins 5th ed. Pages: 128-131

Question 24

15192 – Malignant conditions usually associated with chromosomal translocation include
1: medullary carcinoma of the thyroid
2: chronic myeloid leukaemia
3: Burkitt’s lymphoma
4: carcinoma of the breast

Answer 24

FTTF
Refer to Robbins, 6th Ed, Ch 8, page 284-286

Question 25

13986 – S: The possession of an X chromosome in excess of the normal
complement is less harmful than the possession of an extra autosome
because R: only one X chromosome in a cell is functional

Answer 25

S is true, R is true and a valid explanation of S
Refer to Robbins, 6th Ed, Ch 6, page 173

Question 26

17725 – S: Major karyotype/chromosomal abnormalities are not thought to be a primary event in human neoplasms because R: in human neoplasms, any karyotype abnormalities are uncommon and always variable within the same tumour type.

Answer 26

both S and R and false

Question 27

17719 – S: Karyotype/chromosomal abnormalities are thought to be a primary event in development of many human neoplasms because R: in certain types of human neoplasia, karyotype abnormality is non-random and common in that tumour type.

Answer 27

S is true, R is true and a valid explanation of S
‘Nonlethal genetic damage lies at the heart of carcinogenesis.’ Robbins 6th Ed Chapter 8, page 277.
‘… karyotypic alterations … are found in many … cancerous cells … are gene changes present in all ‘…With each passing year, it becomes more certain that the malignant cells of most types of human cancers have chromosomal abnormalities and … defects are consistent ‘’
The most common types of nonrandom structural abnormalities in tumour cells are:
(a) balanced translocations,
(b) chromosomal deletions, and
(c) cytogenetic manifestations of gene amplification.
Robbins 5th Edition, Chapter 7, page 258.

Question 28

19426 – In the case of a woman who is heterozygous for a recessive X-linked
disorder
A. the abnormal allele is preferentially inactivated in her cells
B. the diagnosis can be made by chromosomal banding studies
C. the disorder may be partially expressed
D. all of her sons will be affected
E. Barr bodies will not be detectable

Answer 28

C
Robbins 6th ed. Pages: 146

Question 29

12536 – A young man is diagnosed as having red-green colour blindness. Of his relatives, the one LEAST likely to carry (or to manifest the effects of) the relevant gene is his
A. father
B. mother
C. maternal grandfather
D. maternal grandmother
E. daughter

Answer 29

A
Red-green colour blindness is caused by a gene on the X chromosome. The young man in question received his X chromosome from his mother (B false), and will transmit his own X chromosome to his daughters (E false), but not to his sons, who receive his Y chromosome. His mother presumably received the gene either from her father (C false), who had the disease, or from her mother (D false), who was a carrier. The patient is male, so could not have received an X chromosome from his father (A true).

Question 30

12954 – The term mutation includes
1: loss of a single nucleotide base
2: loss of a whole gene
3: addition of a single nucleotide base
4: substitution of one nucleotide base for another

Answer 30

TTTT
The term mutation simply means a change in the genetic code. This can be effected by any of the means listed in the question.

Question 31

21763 – The technique of Southern blot analysis
1: involves separation of DNA sequences according to size
2: will not allow identification of heterozygote carriers of autosomal recessive disorders
3: involves amplification of the target DNA sequence with DNA polymerase
4: may be used to detect abnormalities due to point mutations

Answer 31

TFFT
Robbins 5th ed. Pages: 165-169

Question 32

19126 – The polymerase chain reaction
A. involves amplification of the target DNA using an RNA primer
B. is a very sensitive technique for the detection of HIV
C. is an ideal quantitative test for the detection of amplified oncogenes
D. cannot detect the presence of an organism after the patient is symptomatic
E. can be used to detect increased transcription of a normal gene

Answer 32

B
Selected Topics: D13, D29-30.

Question 33

14696 – Fluorescence in situ hybridisation (FISH)
1: generally requires induction of mitosis
2: enhances karyotyping
3: can identify intragene deletion
4: requires repetitive use of individual DNA probes

Answer 33

FTTF
Refer to Robbins, 6th Ed, Ch 6, page 166-168