Describe the major difference between sex determination in Drosophila and in humans.

Key Concepts

Sex Determination Mechanisms

Sex determination refers to the biological system that determines the development of sexual characteristics in an organism. In Drosophila (fruit flies), sex is determined by the ratio of X chromosomes to autosomes, while in humans, it is determined by the presence of specific sex chromosomes (XX for females and XY for males).

X:A Ratio in Drosophila

In Drosophila, the X:A ratio is crucial for sex determination. This ratio compares the number of X chromosomes to the number of sets of autosomes. A ratio of 1 (one X chromosome for each set of autosomes) results in a female, while a ratio of 0.5 (one X chromosome for two sets of autosomes) results in a male, showcasing a unique genetic mechanism distinct from that of humans.

Chromosomal Sex Determination in Humans

Humans utilize a chromosomal sex determination system where the presence of the Y chromosome typically determines male sex. The SRY gene located on the Y chromosome initiates male development, while the absence of a Y chromosome leads to female development. This system contrasts with Drosophila's X:A ratio, highlighting different evolutionary adaptations in sex determination.