Question

Calvin bridges stated that instead of XY chromosomes, sex is determined by the genic balance. What would be the sex of drosophila having XX + 3A and XY + 3A karyotype respectively?

• A. Inter sex and super female
• B. Metafemale and intersex
• C. Intersex and normal male
• D. Intersex and super male

Answer 1

The correct option is D Intersex and super male

In Drosophila, the ratio between the X chromosome and autosome determines the sex of the individual. This was worked by CB Bridges in 1922 on triploid Drosophila. He experimented on triploids on the basis of which he developed his ratio of sex determination or the genic balance theory. According to him, in Drosophila:

• X chromosome is responsible for female characteristics.
• Y chromosome is responsible for the male characteristics.
• Autosome is necessary for the fertility of sex but not responsible for any sex determination.

Thus, according to him, the delicate balance the X chromosome and autosomes is responsible for sex determination.

If the ratio between X and A is:

1.0: it will be a female

0.5: it will be a male

>1 : it will be a super female

<0.5 : it will be a super male

between 0.5 and 1: it will be inter sex.

Hence, for XX + 3A, X/A = 2/3 = 0.6 which is in between 0.5 and 1. So, it is intersex.

For XY + 3A, X/A = 1/3 = 0.3 which is less than 0.5. So, it is a super male.

So, the correct answer is 'intersex and super male'.