Question

Drosopohila 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 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 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. 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.

Thus, the correct answer is option D.