Until puberty, testis cord remains solid. The Wolffian duct differentiates when the Leydig cells in the testis make testosterone. Hence the name cortical sex cord. Cluster of cords surrounds the germ cells. Ova are surrounded by follicle cells, which are formed by the combination of the granulosa cells and thecal cells.
Wolffian duct degenerates because it is deprived of testosterone.
Small arm of the Y chromosome contains the major gene for testis determination. In this region, there is male specific DNA sequence. This sequence encodes a 223 amino acid peptide that could be a transcription factor because it has a HMG box domain. Expressed in the genital ridge before or during testis differentiation. Looked at homologous gene in mice.