250+ TOP MCQs on Chromosomal Abnormalities : Deletion and Answers

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Cytogenetics Multiple Choice Questions on “Chromosomal Abnormalities : Deletion”.

1. Deletion in sex chromosome is better tolerated than that in autosome.
A. True
B. False
Answer: A
Clarification: There are greater possibilities of survival with deletion of genes in sex chromosome, than that in case of autosomal deletion.

2. How will you recognize a terminal deletion from breakage and loss at the terminal end?
A. Indistinguishable
B. Terminal break will lead to shorter chromosome than that due to chunk deletion
C. Terminal break will be sticky
D. Deletion will be recognized by trans factors
Answer: C
Clarification: In terminal deletions the telomere is present; it is sort of removing the bases before telomere not including it. Terminal breaks will however lack telomerase and will be sticky. Shortening in both cases could be similar.

3. What will be the effect of the deletion mutation of a gene at the telomere?
A. Organism will dye
B. Organism will develop serious hazards due to absence of the gene and its product
C. Mild effect on the phenotype
D. No effect
Answer: D
Clarification: The genes at the telomere are silenced, and never expressed. It is in form of heterochromatin inaccessible to the transcription machinery. Thus, deletion of a gene that wasn’t expressed to start with doesn’t make much difference.

4. You hybridize two cells one of which carries a deletion mutation on chromosome 1. What will you expect to observe?
A. Buckling of chromatin of 1st cell
B. Buckling of chromatin of 2nd cell
C. Twisting and loop formation between the two chromatins
D. No observable difference

Answer: B
Clarification: As chromosome 1 of 1st cell carries the deletion it will have less genes than that of the counterpart on the 2nd cell. There will be an error in a pairing where the extra part of 2nd cell chromatin corresponding to the deleted gene will buckle.

5. Which of the following is not a possible cause of lethality of individuals carrying a deletion mutation?
A. Genes that are not haplo sufficient doesn’t produce adequate gene product
B. Genomic imbalance
C. Unmasking of lethal recessive alleles
D. Lack of diversity
Answer: D
Clarification: With the other reasons being true, lack of diversity affects at population level not at individual level. It is no cause for lethality of individuals with deleterious mutation.

6. The appearance of a recessive phenotype due to deletion of dominant gene is called_______________
A. Hemi-dominance
B. Pseudo dominance
C. Imperfect dominance
D. Co-dominance
Answer: B
Clarification: Pseudo dominance is the condition when the recessive allele is expressed in deletion mutation of dominant. Hemi-dominance is the condition when only one copy of the gene is supposed to be present, as in genes of Y chromosomes. Co-dominance and imperfect dominance are different.

7. You generate a fluorescent probe against a gene that has been deleted. You expose the DNA to the probe and observe it under fluorescent microscope. What will you see?
A. Fluorescence will correspond to the gene of interest
B. There will be a number of regions that emit fluorescence
C. Most parts of the chromosome emits fluorescence
D. Nothing is seen under fluorescence microscope

Answer: D
Clarification: The gene corresponding to the probe labeled with fluorescence is deleted. Thus, probe can’t bind the DNA. In this case no fluorescence should be seen on the chromosome.

8. Deletions in chromosomes give the following data-

		Region of deletion  	Gene A activity
		A1			+++
		A2			++
		A3			+
		A4			+++
		A5			+++

Where is the gene located?
A. A1
B. Within A2 and A3
C. Within A4 and A5
D. Between A3 and A4
Answer: B
Clarification: As deletion of A2 and A3 shows slight reduction in gene activity, there is a possibility that the gene is located within these regions. It is not necessary the gene is covering the entire region. The +++ denote full gene activity so it is not effecting gene.

9. Deletion of a region led to over expression of a gene X. What do you conclude from this observation?
A. Part of gene X is mutated
B. Promoter of gene X is deleted
C. Regulator of gene X is deleted
D. No effect on gene X or its regulators
Answer: C
Clarification: In this case over expression of gene X is due to deletion of some negative regulator like operon, insulator, silencer etc.

10. Yellow colour of mouse is generated by _________ mutation.
A. Duplication
B. Deletion
C. Inversion
D. Translocation
Answer: B
Clarification: Here the agouti allele which is to be expressed only in certain tissues is brought under the control of Rally gene promoter which is expressed in all tissues, by deletion of Rally gene and agouti promoter in between the two. The strong promoter over expresses Agouty gene leading to the color.

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11. Which of the following is not true about the Notch gene in Drosophila?
A. It causes a special indentation of the wing margin
B. It is expressed in heterozygous form
C. Notch is lethal in homozygous form
D. Notch is recessive to Facet
Answer: D
Clarification: Facet is expressed only in absence of Notch gene by deletion, thus it is pseudo dominant and recessive to the notch gene. Other options are true, notch is also lethal in hemizygous condition.

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