Genital system

Sex determination

The genital system consists of gonads, internal genital ducts and external genitalia. A person's sex is distinguishable in stages. The chromosomal or genetic sex is established by fertilization (Fertilization and pre-implantation stage). It is determined by the sex chromosomes, and becomes recognizable by the occurrence of the sex chromatin in the nuclei of female cells; this occurs extra-embryonically at S6/S7 and intra-embryonically at about S8. Nevertheless, development in both male and female first goes through a morphologically indifferent stage. Sexual differentiation of the gonads (gonadal sex) first occurs at the beginning of week 7. Differentiation of the gonads in the male occurs under the influence of TDF (Testis Determining Factor), whose transcription is attributed to a gene located on the Y-chromosome (sex determining region of Y, SRY). The somatic sex (genital ducts and external genitalia), and later the psychic sex appear under the influence of the gonadic hormone production (androgens).