Question

Drosophila flies with XXY genotype are females, but human beings with such genotype are abnormal males. It shows that:

• A. Y chromosome is essential for sex determination of Drosophila.
• B. Y chromosome is female determining in Drosophila.
• C. Y chromosome is male determining in human beings.
• D. Y chromosome has no role in sex determination either in Drosophila or human beings.

Answer 1

The correct option is C Y chromosome is male determining in human beings.

'Genic Balance Theory' was proposed by C.B. Bridges in 1922 for sex determination in Drosophila. It states that the ratio of the number of X-chromosomes to that of a complete set of autosomes determines the sex of Drosophila. According to this theory of sex determination, if the ratio of the X chromosome to a total number of sets of autosomes (X/A) is > 1, the organism will be super female. If the ratio of the X chromosome to a total number of sets of autosomes (X/A) falls between 1 and 0.50, the genotype will show an intersex phenotype. The X/A value is 1.0 for normal females and 0.5 for normal males. It clearly shows that in Drosophila autosome bear genes which incline for maleness and X chromosome bear genes which incline for femaleness; Y-chromosome does not play any role in sex determination in Drosophila. It makes options A and B wrong. The presence of Y-chromosome in humans determines the male sex and its absence results in the female sex. Human males carry XY and females carry XX sex chromosomes. Option D is wrong and C is correct.

Thus, the correct answer is option C.