Question

Given below is the karyotype of Drosophila. On the basis of genic balance theory of C.B. Bridges, the sex of this fly would be:

A. Super female
B. Super male
C. Intersex
D. Fertile female

Answer 1

Hint: The formation of male and female individuals or the development of male and female organs of an individual is called sex determination. The Genic balance theory of sex was proposed by Bridges in the year 1926 and he worked on Drosophila. Drosophila also have X and Y chromosomes.

Complete answer:
In Drosophila, for determining the sex, Genic balance theory is used.
According to genic balance theory, sex is determined by balance or by calculating the ratio between number of X-chromosomes and autosome genomes that means X/A ratio.
When the ratio is 1, the sex will be female, when the ratio comes out to be 0.5, the sex of the fly will be male. If the ratio is between 1 and 0.5 then the fly will be intersex. If the ratio is greater than 1, then the individual will be metafemale and if it is less than 0.5, then it will be metamale.
In the given diagram, we can clearly see the number of X-chromosomes are 2 and number of autosomes are 3. So, the ratio becomes 2:3 which is equal to 0.66 that means, the given individual is intersex.

So, the correct answer is option (c).

Note:
The sex determination is basically of two types: chromosomal sex determination and non-genetic sex determination. In humans and Drosophila, chromosomal sex determination is used. Drosophila is commonly used in many laboratory experiments because $75\%$ of genes that cause disease in humans are also found in Drosophila. And also they have short and simple reproductive cycles.