This set of Cytogenetics Multiple Choice Questions on “Silencing and Genomic Imprinting”.
1. Genomic imprinting in autosomes is seen in _________________ percent of the genes.
A. 100%
B. 50%
C. 25%
D. <1%
Answer: D
Clarification: In autosomes most of the alleles can be expressed from both the parents. But a very shoet part i.e. <1% shows genomic imprinting.
2. Differential expression of the genetic material depending on its parentage of inheritance gives____________
A. Penetrance
B. Expressivity
C. Imprinting
D. Non-penetrance
Answer: C
Clarification: Genomic imprinting states that the alleles of some genes vary in their or expression depending on the fact that they are inherited from the mother or the father.
3. In Igf2 of human ______________ allele is expressed, and Igfr of mice __________ allele is expressed.
A. Maternal, maternal
B. Paternal, paternal
C. Maternal, paternal
D. Paternal, maternal
Answer: D
Clarification: The insulin like growth factor Igf for human shows that there only the paternal allele is expressed, but in its receptor, in case of mice the maternal allele is expressed. Thus both the alles must be present for proper function of the signal.
4. Which of the following doesn’t agree with XIST?
A. It codes for an mRNA that coats the inactive X chromosome into a bar body
B. It is the only gene that is active in inactive X chromosome
C. The embryo cells shows that maternal allele XIST is active over paternal
D. Inactivation is seen in somatic cells
Answer: C
Clarification: XIST allele in case of the embryo doesn’t show any imprinting. Imprinting is seen in case of the extra-embryonic cells.
5. The imprinting of genes has an epigenetic mode of regulation.
A. True
B. False
Answer: A
Clarification: Imprinting is ascertained by the methylation of certain C residues in CpG islands in the promoter region of a gene. Thus, it is not genetic but epigenetic regulation.
6. Choose the wrong statement in the regulation of imprinting.
A. Methylation of the C residues are seen in the CpG islands
B. The methylation prevents binding of the RNA polymerase
C. Genes are methylated at random
D. Deletion of gene with methylated CpG islands will have no effect
Answer: C
Clarification: In the case of imprinting which of the allele’s CpG island is methylated depends on the parent from which it is inherited. This shows that the methylation is not random but related to imprinting.
7. In mice if you delete the Igf2 gene from a female, the progeny will_____________
A. Be smaller
B. Die
C. No major change
D. Be larger
Answer: C
Clarification: In mice the Igf2 genes from the female parent is methylated and inactivated by imprinting and only the male one is expressed. Thus, absence of the respective gene in mother shows no significant effect. However, if it were male hen the progeny would be smaller.
8. In mice H19 and Igf2 genes are controlled by the same enhancer. Which of the following is true?
A. The enhancer enhances both the gene on promoter binding
B. In one chromosome both the genes are expressed and in other they are not
C. Igf2 shows paternal imprinting, H19 shows maternal imprinting
D. Both the genes show paternal imprinting
Answer: C
Clarification: It is much of a surprise although both the genes can be enhanced by the same enhancer element located downstream of H19 both are not enhanced at once. In maternal gene the H19 is expressed and in paternal gene the Igf2 is expressed.
9. In mice the expression of Igf2 and H199 is only controlled by methylation.
A. True
B. False
Answer: B
Clarification: In addition to methylation the control is achieved by the presence of an insulator CTCB that helps by preventing the enhancer interaction of Igf2 in the maternal chromosome.
10. Choose the wrong statement from the following.
A. Maternal Igf2 is methylated to prevent expression
B. Paternal H19 is methylated to avoid expression
C. The enhancer can lead to expression of H19 in maternal gene
D. The enhancer can’t lead to expression of Igf2 in paternal gene
Answer: A
Clarification: It is true that the maternal Igf2 is not expressed in mice but the mechanism is via blockage of the enhancer by an insulator called CTCB binding to the CCCTC sequence in between the two adjacent genes. Rest of the options is correct.
11. During _________________ both the H19 alleles are ___________________
A. Oogenesis, inactivated
B. Oogenesis, activated
C. Oogenesis, hyper-activated
D. Spermatogenesis, activated
Answer: B
Clarification: The genomic imprinting has to be reset in every generation. This is achieved via the means that the genes that are maternally inherited are activated during oogenesis and paternally inherited genes are inactivated during the same and reverse for spermatogenesis. H19 is maternally inherited.
12. What will happen if an individual receives two copies of a gene from the same parent?
A. UPD
B. One gene will be automatically inactivated
C. Both the genes will show their product
D. Nothing much will be seen