BRIDGES’ THEORY OF SEX DETERMINATION IN DROSOPHILA

Introduction to Drosophila Sex Determination

Drosophila melanogaster, commonly known as the fruit fly, has been a model organism for genetic studies for over a century. One of the fundamental aspects of Drosophila genetics is its sex determination system. In Drosophila, sex is determined by the presence or absence of the Y chromosome, unlike in mammals where it is determined by the presence of X and Y chromosomes.

Discovery of Sex-Linked Genes

In the early 20th century, Calvin Bridges conducted groundbreaking research on Drosophila sex determination. He discovered that certain traits in Drosophila, such as eye color, were linked to the sex chromosomes. This led him to propose a theory of sex determination in Drosophila based on the behavior of these sex-linked genes.

Bridges’ Theory

Bridges proposed that in Drosophila, sex is determined by the ratio of X chromosomes to autosomes rather than by the presence of a Y chromosome as in mammals. According to his theory, the X:A ratio determines whether an individual develops as male or female. Specifically, he suggested that a 1:2 ratio results in a male phenotype, while a 1:1 ratio leads to a female phenotype.

Supporting Evidence

Bridges’ theory was supported by his observations of unusual sex chromosome configurations in Drosophila. He observed cases where individuals with extra X chromosomes developed as females despite having more than one X chromosome. This provided evidence for the role of X chromosome dosage in determining sex.

Legacy and Impact

Bridges’ theory laid the foundation for understanding sex determination and dosage compensation mechanisms in Drosophila. Subsequent research has further elucidated the molecular mechanisms underlying sex determination in this model organism, building upon Bridges’ pioneering work.

In summary, Bridges’ theory of sex determination in Drosophila proposed that the ratio of X chromosomes to autosomes determines the sex of an individual, with a specific X:A ratio leading to male or female phenotypes.