Question

Drosophila is metamale with chromosomal formulation.

• A. $2A+3X$
• B. $3A+3X$
• C. $4A+3X$
• D. $3A+XY$
• E. $2A+XY$

Answer 1

The correct option is D $3A+XY$

'Genic Balance Theory' was proposed by C.B. Bridges in 1922 for sex determination in Drosophila. It states that the ratio of number of X-chromosome to that of a complete set of autosome determines the sex of Drosophila. According to this theory of sex determination, if the ratio of the X chromosome to a total number of sets of autosomes (X/A) is > 1, the organism will be super female. If the ratio of the 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. The X/A ratio < 0.5 gives supermale or metamale. Drosophila with 3 X chromosomes and 2 sets of autosomes have the (X/A= 3/2) ratio of 1.5 and shows superfemale phenotype. Option A is the incorrect answer. Drosophila with 3 X chromosomes and 3 sets of autosomes have the (X/A = 3/3) ratio of 1 and is female; option B is the incorrect answer. Drosophila with 3 X chromosomes and 4 set of autosomes have the (X/A = 3/4) ratio of 0.75 and is intersex; option C is the incorrect answer. Drosophila with 1 X chromosome and 3 set of autosomes have the (X/A = 1/3) ratio of 0.33 and is metamale; option D is the correct answer. Drosophila with 1 X chromosome and 2 set of autosomes have the (X/A = 1/2) ratio of 0.5 and is male; option E is the incorrect answer.

So, the correct answer is '3A+XY'.