Establishing sexual dimorphism in humans.

Sexual dimorphism, i.e. the distinct recognition of only two sexes per species, is the phenotypic expression of a multi-stage procedure at chromosomal, gonadal, hormonal and behavioral level. Chromosomal--genetic sexual dimorphism refers to the presence of two identical (XX) or two different (XY) gonosomes in females and males, respectively. This is due to the distinct content of the X and Y-chromosomes in both genes and regulatory sequences, SRY being the key regulator Hormones (AMH, testosterone, Insl3) secreted by the foetal testis (gonadal sexual dimorphism), impede Müller duct development, masculinize Wolff duct derivatives and are involved in testicular descent (hormonal sexual dimorphism). Steroid hormone receptors detected in the nervous system, link androgens with behavioral sexual dimorphism. Furthermore, sex chromosome genes directly affect brain sexual dimorphism and this may precede gonadal differentiation.