Cytogenetics Questions and Answers – Multiple Alleles


This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Multiple Alleles”.

1. If there are multiple alleles for a gene which of the following is true?
a) All the alleles same expressed at the same time
b) Among the multiple copies resent only the most dominant one is expressed
c) Only two alleles are present at a time
d) Only one allele is dominant rest all are recessive
View Answer

Answer: c
Explanation: If a gene has multiple allele then there are varied dominance recessive relations but ultimately one organism has only 2 of these multiple alleles and the relation among them determines the phenotype.

2. Multiple alleles arise from the same allele by mutation.
a) True
b) False
View Answer

Answer: a
Explanation: Multiple alleles have a common origin- i.e. the wild type gene. Mutations in these wild type gene leads to different phenotypic expressions and dominance recessive relations.

3. If there are 4 alleles for a gene, then what would be the number of genotypes?
a) 5
b) 10
c) 15
d) 20
View Answer

Answer: b
Explanation: The number of genotypic expression in multiple allele series is given by the formula 0.5[n(n+1)], where n is the number of alleles. So here it would be 10.
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4. ABO blood group is not an example of ______________
a) Co dominance
b) Multiple allele
c) Epistasis
d) Mendalian relations
View Answer

Answer: c
Explanation: In ABO blood group there are three alleles IA IB IO. Where he 1st two are codominant and the 3rd is recessive to the rest. However, they don’t show epistasis.

5. Like ABO blood group, MN blood group also shows multiple allelism.
a) True
b) False
View Answer

Answer: b
Explanation: In MN blood group system there are only two alleles M and N which are codominant. Thus, this is not an example of multiple alleles but ABO blood grouping is.

6. In drosophila eye color is determined by multiple allele systems. Which of the following sequence is true for the dominance relationship?
a) Eosin > red > white
b) Red > eosin > White
c) White > red > eosin
d) Eosin > white > red
View Answer

Answer: b
Explanation: In case of dominant recessive relations among eye colour in Drosophila, Red is the wild type which is dominant over eosin and white. Eosin on the other hand is also dominant over white.

7. If a person had Hh in the H antigen locus and IA i in the blood group locus what would be the blood group?
a) A
b) B
c) AB
d) O
View Answer

Answer: a
Explanation: In heterozygous condition, the H antigen is effectively produced by the gene which results in the expression of the blood group of the blood group locus. Here the blood group expressed is O.

8. If a mother has blood group O and father has blood group A, the child being type AB, which of the following is wrong?
a) The mother may have IB allele that is passed to daughter
b) The father of the child is someone else with AB blood type
c) The child has IA allele and also IB allele
d) This is an abnormal case
View Answer

Answer: b
Explanation: Even if the father was someone with AB blood type is not possible for one parent to give both the alleles to their child. This is more likely a case of Bombay blood group where the mother is homozygous for the h antigen and her blood group is not expressed.

9. IA allele codes for the _________________ while IB codes for _________________
a) Alpha N galactosamine transferase, galactose transferase
b) Glycosamino glycan transferase, Alpha N glucosamine transferase
c) Alpha glucosamine transferase, Alpha galactosamine transferase
d) Galactose transferase, galactose transferase
View Answer

Answer: a
Explanation: The IA allele produces a glycosyltransferase enzyme that adds the sugar α N-acetyl galacto-samine to the polysaccharide to produce the A antigen. The IB allele produces a different glycolsyl transferase enzyme that adds the sugar galactose to produce the B antigen.

10. The eye color of drosophila is _______________
a) Autosomal
b) Codominant
c) X linked
d) Y linked
View Answer

Answer: c
Explanation: The eye color gene of drosophila is located in the X chromosome, so it is X linked and shows the respective mode of inheritance.

11. Which of the following is true wrong about ABO blood group?
a) It determines the antigen on RBC
b) Some people may secretes a soluble form of this
c) Secretors have se/se gene combination for secretion locus
d) Non- secretors don’t produce this soluble form
View Answer

Answer: c
Explanation: Secretors is a dominant phenotype hence Se/Se and Se/se are both secretors, while the genotype in option c se/se is for non-secretors. The rest of the options are true.

12. If a wild type eyed female drosophila is crossed to a white eyed male, what will be the percentage of their progeny with white eyes.
a) 1
b) None
c) Half
d) 1/4
View Answer

Answer: b
Explanation: Eye colour is present on the X chromosome , so the females of F1 will be heterozygous red eyed(wild-type), and the males will have only one eye colour allele from mother which would be for red eyes.

13. If you cross a red eyed male with a white eyed female, all the sons would be ___________ and all the daughters would be ______________
a) Red eyed, red eyed
b) Red eyed, white eyed
c) White eyed, White eyed
d) White eyed, red eyed
View Answer

Answer: d
Explanation: he F1 daughters would be heterozygous as they get the red allele from mother and white from father- producing red eyes. The sons would have only eye colour allele from mother that would give white eye colour.

14. If you cross a eosin male Drosophila with a red eyed female, the daughters would have________________
a) Eosin eye
b) Red eye
c) White eye
d) No eye colour
View Answer

Answer: b
Explanation: Eosin eye colour is recessive to red eye colour. The daughters which are heterozygote would have one copy of each allele and thus will have red eye colour.

15. If a Drosophila is having XXY sex chromosomal combination with one X bearing white allele for eye colour and another X having eosin allele for eye colour, what would be its phenotype?
a) This is a lethal combination
b) White eyes
c) Red eyes
d) Eosin eyes
View Answer

Answer: d
Explanation: Eosin eye colour is dominant over white eyes. In this case, the combination is not lethal and the fly is a female with eosin eye colour.

Sanfoundry Global Education & Learning Series – Cytogenetics.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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