This page has been archived and is no longer updated. Whether an animal will become a male, a female, or a hermaphrodite is determined very early in development. Scientists have worked for hundreds of years to understand the sex-determination system. For instance, in B. If the male's heat could overwhelm the female's coldness, then a male child would form. In contrast, if the female's coldness was too strong or the male's heat too weak , a female child would form.
Sex determination in Drosophila
Genetic Mechanisms of Sex Determination | Learn Science at Scitable
The two broadest categories are genetic sex determination GSD , in which the sex of offspring is set by a sex chromosome or an autosomal gene, and environmental sex determination ESD , in which sex is determined by temperature as with turtles , local sex ratio as with some tropical fish , or population density as with mermithid nematodes. Though little is known about the molecular mechanisms of ESD, within the GSD systems many different mechanisms have been uncovered. There are also systems in which heterozygosity at a single locus is required for female development known as complementary sex determination , as well as systems involving sex determination via multiple genes with additive effects Haag, ; see full text of article. Molecular genetic investigations of GSD in model systems such as Drosophila , Caenorhabditis , and mice have revealed a clear lack of conservation, underscoring the diversity.
Genetic Mechanisms of Sex Determination
Drosophila melanogaster is a species of fly the taxonomic order Diptera in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting with Charles W. Woodworth 's proposal of the use of this species as a model organism , D. As of , six Nobel prizes had been awarded for research using Drosophila.
One of the most important decisions in development is whether to be male or female. In Drosophila melanogaster , most cells make this choice independent of their neighbors such that diploid cells with one X chromosome XY are male and those with two X chromosomes XX are female. X-chromosome number is relayed through regulatory proteins that act together to activate Sex-lethal Sxl in XX animals. The resulting SXL female specific RNA binding protein modulates the expression of a set of downstream genes, ultimately leading to sexually dimorphic structures and behaviors. Despite the apparent simplicity of this mechanism, Sxl activity is controlled by a host of transcriptional and posttranscriptional mechanisms that tailor its function to specific developmental scenarios.