Which chromosome pair determines sex in Drosophila?
1st pair
2nd pair
3rd pair
4th pair
The second pair of chromosomes in Drosophila is the pair that controls sex. The proportion of X chromosomes to the total number of sets of autosomes (A) in Drosophila is used to identify gender. Drosophila has X and Y sex chromosomes, with females having XX and males having XY. The quantity of X chromosomes in the 2nd chromosome pair determines the ratio of sets of autosomes to X chromosomes. For instance, a female fly is produced when the ratio is 1:1 (i.e., 1 X chromosome to 2 sets of autosomes), whereas a male fly is produced when the ratio is 1:2 (i.e., 1 X chromosome to 4 sets of autosomes). Therefore, in Drosophila, the fly's sex is determined by the 2nd pair of chromosomes.
Option 2 is the correct answer.