Drosophila melanogaster, a model organism in genetics, exhibits a unique mechanism of sex determination primarily explained by the Genic Balance Theory. This theory, proposed by Calvin Bridges, is based on the ratio of X chromosomes to sets of autosomes, commonly referred to as the X:A ratio. In Drosophila, the X:A ratio determines sexual development rather than the mere presence of a Y chromosome. A ratio of 1.0, such as in individuals with two X chromosomes and two sets of autosomes (XX; 2A), leads to female development. A ratio of 0.5, as seen in XY; 2A individuals, results in male development. Intermediate ratios, like 0.67 (XXY; 3A) or 0.33 (X; 3A), produce intersex or sterile individuals, illustrating that both the X chromosome number and autosomal complement influence sex determination. Calvin Bridges’ experiments with Drosophila provided critical evidence for the Genic Balance Theory. Bridges performed genetic crosses and induced chromosomal aberrations such as nondisjunction of the X chromosome. He observed that flies with varying numbers of X chromosomes relative to autosomes displayed predictable sexual phenotypes. For instance, an XXY fly with a 1.0 X:A ratio developed