Question

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In ________, sex is determined by the ratio of the number of X chromosomes to the number of
haploid sets of autosomes.
A) reptiles
B) Drosophila
C) humans
D) C. elegans
E) Drosophila and C. elegans

Answer 1

In Drosophila, sex is determined by the X:A ratio where X refers to the number of X chromosomes and A refers to the number of haploid sets of autosomes. Two X chromosomes to two sets of autosomes results in a female, whereas one X chromosome to two sets of autosomes results in a male.

Step-by-step explanation:

In the fruit fly Drosophila melanogaster, sex determination is based on the ratio of the number of X chromosomes to the number of haploid sets of autosomes (X:A ratio). Females typically have two X chromosomes (XX) and males have one X and no Y chromosome (XO). This system is different from humans, where females are XX and males are XY, and the presence of a Y chromosome determines maleness.

In Drosophila, the balance between the autosomes and the number of X chromosomes results in the development of sexual characteristics. If the ratio is 1.0 (two X chromosomes to two sets of autosomes, or XX:AA), the fly develops as female. If the ratio is 0.5 (one X chromosome to two sets of autosomes, or X:AA), the fly develops as male. This chromosomal mechanism of sex determination is unique to Drosophila and some other organisms such as C.