Practice question

Mammalian Y chromosome harbors Sry gene considered testis-determining factor. Presence of Y means presence of Sry whose timely expression in genital ridge precursors between six to seven weeks upregulates Sox9 in pre-Sertoli cells, activating Fgf9 loop, testis cord formation, anti-Müllerian hormone secretion and testosterone synthesis from Leydig cells. Wolffian ducts thus persist while Müllerian ducts regress, generating male phenotype. Absence leaves ovarian pathway established via Wnt4/Rspo1/β-catenin directing ovary formation. Therefore presence of Y chromosome leads anatomically and molecularly to development of testes in normal mammals.