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

Verified step by step guidance

1. Understand that sex determination is the biological system that determines the development of sexual characteristics in an organism.
2. Recognize that in humans, sex determination is primarily based on the presence or absence of the Y chromosome: individuals with XY chromosomes develop as males, and those with XX chromosomes develop as females.
3. Note that in Drosophila (fruit flies), sex determination depends on the ratio of X chromosomes to sets of autosomes (non-sex chromosomes), rather than the presence of a Y chromosome.
4. Specifically, in Drosophila, a ratio of X chromosomes to autosome sets of 1.0 (e.g., 2X:2 sets of autosomes) results in a female, while a ratio of 0.5 (e.g., 1X:2 sets of autosomes) results in a male.
5. Summarize that the major difference is that humans use a chromosomal system based on the presence of the Y chromosome for sex determination, whereas Drosophila use the X chromosome to autosome ratio to determine sex.

Key Concepts

Sex Determination in Drosophila

In Drosophila, sex is determined by the ratio of X chromosomes to sets of autosomes (X:A ratio). A ratio of 1.0 (e.g., XX) results in a female, while a ratio of 0.5 (e.g., XY) results in a male, regardless of the presence of a Y chromosome.

Sex Determination in Humans

Human sex determination depends on the presence or absence of the Y chromosome. Individuals with an XY chromosome pair develop as males due to the SRY gene on the Y chromosome, while XX individuals develop as females.

Role of Chromosomes vs. Chromosome Ratios

The key difference lies in the mechanism: Drosophila uses the X-to-autosome ratio to determine sex, making the Y chromosome non-essential for maleness, whereas humans rely on the presence of the Y chromosome and its genes to trigger male development.