Final answer:
Transcription factors such as the human SRY gene and the Drosophila Sex lethal (Sxl) gene drive the production of male and female tracts by regulating gene expression and influencing the development of sexual characteristics.
Step-by-step explanation:
The production of male and female tracts is driven by the interaction and activity of various transcription factors that regulate gene expression, determining sexual characteristics in organisms. In humans, the SRY gene is pivotal for initiating male trait development. Located on the Y chromosome, the SRY gene produces the testis-determining factor which directs the bipotential gonadal tissue to develop into testes, leading to a cascade effect that culminates in the formation of the male reproductive system. In the absence of the SRY gene, as seen in typical female XY genotype, this results in the development of ovaries and subsequently the female reproductive system.
Similarly, in fruit flies, such as Drosophila melanogaster, the Sex lethal (Sxl) gene plays a crucial role in sexual differentiation. The Sxl gene triggers a series of splicing events, with the transformer (tra) gene undergoing differential splicing influenced by the Sxl protein. The presence of the Sxl protein leads to the splicing of tra, dsx, and fru into their female forms, resulting in the formation of female sex traits. Conversely, in the absence of the Sxl protein, the male forms of these genes are produced, leading to male sex characteristics.