Question

In metamale Drosophila, chromosome combination is
(a) 3X: 2A
(b) 3X: 3A
(c) XY: 3A
(d) XY: 2A

Answer 1

Hint: The Genic Balance Theory was proposed by C.B. Bridges for sex determination in Drosophila, in 1922. It expresses that the proportion of the number of X-chromosomes to the total number of sets of autosomes decides the sex of Drosophila.

Complete answer:
In metamale Drosophila, chromosome combination is XY: 3A.
According to the theory of sex determination in Drosophila, if the ratio of X chromosome to a total number of sets of autosomes (X/A) is greater than 1, then the offspring of the Drosophila will be a super female. If the ratio of the X chromosome to that of the total number of sets of autosomes (X/A) falls between 0.5 and 1, then the offspring will exhibit both and female phenotypes. The X/A ratio is 1.0, then the offspring will be for normal females and 0.5 for the normal male. If the ratio of the X chromosome to a total number of sets of autosomes (X/A) is below 0.50, the offspring will be metamale (low viability Drosophila) . The question says that the ratio of X/A is 1/3 that is XY: 3A. When dividing the ratio will come 0.33 which is less than 0.5, hence the offspring will be meta male.
So, the correct answer is, ‘XY: 3A.’

Note: A metamale (or supermale) is a low viability Drosophila fruit fly with a male phenotype. In Drosophila, the ratio of X chromosomes to sets of autosomes (A) is less than half or 0.5. For example, a dragonfly with one X chromosome and two sets of autosomes is a normal male while a dragonfly with one X chromosome and three sets of autosomes is called a metamale.