Question

Data produced by C. Bridges in the early part of this century indicate that sex in Drosophila is

determined by ________.
A) the number of Y chromosomes
B) a balance between the number of X chromosomes and the number of haploid sets of
autosomes
C) the ratio of X to Y chromosomes
D) the number of X chromosomes
E) the SRY gene

Answer 1

Sex in Drosophila is determined by a balance between the number of X chromosomes and the number of haploid sets of autosomes, or the X/A ratio, which influences the transcription of the Sex lethal (Sxl) gene and subsequent sex-specific protein production.

Step-by-step explanation:

Data produced by C. Bridges in the early part of this century indicated that sex in Drosophila is determined by a balance between the number of X chromosomes and the number of haploid sets of autosomes. This is also referred to as the X/A ratio (the X chromosome-to-autosome ratio), which is described in the primary sex-determination gene called Sex lethal (Sxl).

Sxl is transcribed only when this ratio equals or exceeds 1, which is the case for females in Drosophila who have two X chromosomes, resulting in the transcription only in females. The presence of Sxl leads to splicing in the transformer (tra) gene, resulting in sex-specific mRNA and subsequently the production of proteins that determine the sex of the individual.