Discussion
Difference in chromosomal determination of sex between Drosophila and human is because :
Answer: A
The difference is that in Drosophila the ratio of X chromosomes to autosomes decides sex, whereas in humans the Y chromosome determines maleness.
In Drosophila an X:A ratio of 1 (XX with two sets of autosomes) gives a female and a ratio of 0.5 gives a male, so an XO fly is a (sterile) male and an XXY fly is a female; the Y is needed only for male fertility. In humans the SRY gene on the Y chromosome switches on testis development, so XXY (Klinefelter) individuals are male and XO (Turner) individuals are female.
The other options reverse the two systems: a mere pair of X chromosomes does not decide sex in the fly, the Y does not determine maleness in Drosophila, and a single X without a Y gives a female, not a male, in humans.
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