This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Sex Determination in Mammals”.
1. Mammals have _______________ type of sex determination.
a) XX/ XY
b) XX/ XO
c) ZZ/ ZY
Explanation: Like Drosophila mammals also have XX/ XY mode of sex determination. However, the mechanism of sex determination in this case is much different.
2. In Drosophila an organism with the genetic composition AA+XXY will be a normal female. What will be the case for mammal?
a) Normal female
b) Normal male
Explanation: IN mammals unlike drosophila the presence of Y chromosome determines maleness, thus XXY will have male characters. Again the presence of additional X chromosome will give rise to some female characters resulting in klinefelter.
3. In mammals which of the following will be a Turner?
a) AA + XXY
b) AA+ XYY
c) AA + XO/ XY
d) AA+ XO
Explanation: AA+ XO will be a turner. This condition the female characters are underdeveloped due to the absence of one X chromosome. AA+ XO/XY on the other hand is intersex.
4. Human being with genetic combination AA+ XXX will be non-viable like Drosophila with the same combination.
Explanation: In human beings unlike drosophila there is dosage compensation for the extra X chromosome. Due to this reason this person will be a viable female.
5. The gene for sex determination in mammals is _________ and it is located in ___________
a) MAT, Y
b) SRY, Y
c) MAT, X
d) SRY, X
Explanation: SRY is the gene in Y chromosome that is necessary for the development of male characters. It is located in the Y chromosome. The MAT is sex determining factor for yeast.
6. In an experiment, you add the short arm of Y chromosome to a cell line with composition AA+ XX. What will you see?
a) The cell rejects the Y chromosome
b) The cell develop female character
c) The cell develop male character
d) The cell develop neuter gender character
Explanation: The short arm of the Y chromosome is carrying the SRY gene which determines the sex of the organism. Thus introduction of Y chromosome will promote the development of male characters.
7. Which of the following is wrong for sex chromosome?
a) X chromosome is larger than Y
b) Female human are homozygous
c) Y chromosome carries TDF
d) All genes present on Y chromosome are unique to it
Explanation: There is a homologous region between the X and Y chromosome, and genes in Y chromosome in that area is not unique to it. TDF is another name used for SRC gene that is also located on Y chromosome.
8. Klinefelter syndrome results due to ____________
a) Non-disjunction in the male gamete
b) Non-disjunction in the female gamete
c) Gradual loss of chromosome
d) Non-disjunction in any of the gametes
Explanation: Klinefelter syndrome results from a genetic combination AA+ XXY; this can result from non-disjunction in either male or female gamete.
9. A person with a genetic composition AA+XYY composition. The non-disjunction is in the __________ parent and in _____________ meiotic division.
a) Male, 1st
b) Male, 2nd
c) Female, 1st
d) Female, 2nd
Explanation: A female can never have Y chromosome to start with so the non-disjunction is in a male. If the non-disjunction was in 1st division improper segregation of X and Y will produce XY gamete. Here there is an improper 2nd division where 2Y generated in meiosis 2 moves to same pole giving YY gamete.
10. A female with AA+ XXX can only result from female parental non-disjunction.
Explanation: Both 1st and 2nd meiotic non-disjunction in female can give AA+ XXX combination. Also 2nd meiotic non-disjunction in male gamete where two X chromosome moves to same pole can also give this result.
11. The intersex is produced by ________________
a) Fusion of a male and female zygote
b) Loss of X chromosome from some cells
c) Loss of Y chromosomes from some cells
d) Gain of X or Y chromosome due to non-disjunction
Explanation: Intersex has the combination AA+ XO/XY. Presence of Y chromosomes develops male character so AA+XY cells are male. Absence of Y gives female characters so AA+XO gives female, this is due to loss of Y chromosome from these cells. Overall it results in intersex.
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