For a full account, readers are referred to the recent monograph by van der Putte (18). Ovaries
Primordial germ cells migrate to the genital ridge to form the gonads. In the fifth-week, the gonads are indifferent and capable of developing into testes or ovaries (19). Gonadal differentiation is achieved through a complex interaction between different expressed genes. The genetic expression of genes on the Y chromosome, particularly SRY, the master regulatory gene, causes the gonad to become a testis. The first sign of testicular development is the presence of Sertoli cells at six to seven weeks. Ovarian development is thought to be related to expression of Dax-1 (20). The first primordial ovarian follicles are seen after 13.5 weeks.
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