Question

Explain how the Y chromosome determines development of the mesonephric duct and not the paramesonephric duct. Be sure to describe the genes involved, what the products of those genes are, and how those gene products influence development of these two reproductive tracts.

Answer 1

Y chromosome consist of Sry gene ( sex related gene on Y) is responsible for the formation of mesonephric duct which is also known as Wolffian duct. The Sox (Sry-type HMG box) genes encode a group of proteins characterized by the existence of an SRY (sex-determining region on Y chromosome) box, a 79 amino acid motif that encodes an HMG (high mobility group) domain which can bind and bend DNA, which is the only part in SRY that is conserved between species.

The differentiation of the gonads is dependent on the presence or absence of the SRY gene on the Y chromosome, which stimulates differentiation of the testes in males by stimulation Testosterone production by Leydig cells which drives the differentiation of the mesonephric ducts into male internal sex organs and dihydrotestosterone drives the differentiation of male external genitalia. Mullerian inhibitory factor (MIF,) is produce by Sertoli cells which suppresses the differentiation of the paramesonephric ducts. The anti mullerian factor or mullerian inhibitory factor is a secretory ligand belongs to class of TGF-beta (transforming growth factor-beta) superfamily of proteins. Ligands of this family bind various TGF-beta receptors leading to recruitment and activation of SMAD family transcription factors that regulate gene expression. The encoded MIF preproprotein is proteolytically processed to generate N- and C-terminal cleavage products that homodimerize and associate to form a biologically active noncovalent complex. This complex binds to the anti-Mullerian hormone receptor type 2 and causes the regression of Mullerian ducts in the male

In females, the absence of MIF allows differentiation of the paramesonephric ducts into the female internal organs, and estrogen drives the differentiation of female external genitalia. The absence of testosterone prevents the differentiation of the mesonephric ducts in females.