Final answer:
Sxl (Sex lethal) acts to inhibit the expression of the Dosage Compensation Complex (DCC) in females of Drosophila melanogaster to prevent the upregulation of the X chromosome gene expression that occurs in males for dosage balance. This mechanism is essential for proper development and parallels the X inactivation process seen in human females.
Step-by-step explanation:
The role of Sex lethal (Sxl) in the expression of the Dosage Compensation Complex (DCC) is to inhibit the expression of DCC in females. Sxl is a splicing repressor that is active in females, as they have two X chromosomes, and it blocks the expression of tra-dependent processes that would otherwise lead to DCC function. Since DCC is involved in upregulating X chromosome gene expression primarily in males, to balance the dosage between the sexes, the inhibition by Sxl ensures that females, who have two X chromosomes, do not have this upregulation and thus prevent overdosage.
Through the inhibition of DCC, Sxl contributes to the mechanism of X chromosome dosage compensation. This process is crucial for maintaining the balance of gene expression from the sex chromosomes and ensuring normal development and functionality in Drosophila. In humans, a similar process of dosage compensation occurs through the inactivation of one X chromosome in females, leading to the formation of a Barr body.