Question

2A+XO genotype in Drosophila will be

• A. normal male
• B. sterile female
• C. normal female
• D. sterile male

Answer 1

The correct option is D sterile male

2A+XO genotype in Drosophila is a sterile male. Sex determination in Drosophila can be explained by genic balance theory. According to this theory, sex is determined by the ratio of number of X chromosomes to autosomal sets. If the ratio is 1 then it is a female fly and if it is 0.5 then it is a male fly.

The ratio of 2A+XO genotype fly is:

$\frac{\text{No. of X chromosomes}}{\text{Sets of autosomes}}=\frac{1}{2}=0.5$

As the ratio is 0.5, it is male, but due to the absence of Y chromosome it is a sterile male. Hence, Y chromosome is essential for fertility of male sex.