Genital ridge

The genital ridge is a structure in early human embryonic development (around week five) that gives rise to the sex cords, the precursors of the reproductive system's gonads . The genital ridge initially consists mainly of mesenchyme and cells of underlying mesonephric origin.

The sex cords differentiate into male and female cords. In the female the sex cords are known as cortical cords, and give rise to the ovary, and in the male are known as testis cords that give rise to the testicle.

Associated genes

Genes associated with the developing gonads can be categorized into those that form the sexually indifferent gonad, those that determine whether the indifferent gonad will differentiate as male or female, and those that promote differentiation into male or female parts. Genes that form the sexually indifferent gonad are SF1 and WT1. Genes that determine sex are SRY, SOX9, and DAX1. Genes driving the differentiation into male or female structures are SF1, WT1, and WNT4. The other genes have roles in development that are not exclusively sex-related.

DMRT1

Evidence suggests that a DM domain gene, DMRT1, is involved in sexual development. This gene is located on chromosome 9. Its location suggests that it is required for the development of testis. XY humans hemizygous for the chromosome 9p, where DMRT1 is located, are often feminized. This feminization can range from ambiguous genitalia to XY sex reversal.

SRY

The genital ridge houses the transcript for SRY, the Y-chromosomal gene responsible for sex determination. The urogenital ridge is made up of the gonadal anlage and the mesonephros. The mesonephros is involved in the development of the testis, but its role is in differentiation, and not determination. This is indicated by the absence of SRY expression in the mesonephros. SRY expression is expressed exclusively in the developing gonad, lacking a presence in any other tissue in embryos or adults.