Q. Determine the sex of Drosophila with the genotype AAA+XX chromosomal constitution :
(a) Normal female
(b) Intersex
(c) Super male
(d) Super female
Solution :
Correct option : B Genic Balance Theory was proposed by C.B. Bridges in 1922 for sex determination in Drosophila. It states that ratio of number of X-chromosome to that of the complete set of autosome determines the sex of Drosophila. According to this theory of sex determination, if the ratio of X chromosome to a total number of sets of autosomes (X/A) is >1, the organism will be super female. If the ratio of X chromosome to a total number of sets of autosomes (X/A) falls between 1 and 0.50, the genotype will show the intersex phenotype. The X/A value is 1.0 for normal female and 0.5 for the normal male. According to the question, Drosophila is having 2 X chromosomes and 3 autosomes which make the X/A ratio 0.66 (between 1 and 0.50) i.e., intersex genotype. Therefore, the correct answer is option B.