Brain sexual differentiation is orchestrated by precise coordination of sex steroid hormones. In some species, programming of select male brain regions is dependent upon aromatization of testosterone to estrogen. In mammals, these hormones surge during the organizational and activational periods that occur during perinatal development and adulthood, respectively. In various fish and reptiles, incubation temperature during a critical embryonic period results in male or female sexual differentiation, but this can be overridden in males by early exposure to estrogenic chemicals. Such rodent species, prototherians monotremes, who also lack Sry , and fish and reptile species that demonstrate temperature sex determination TSD seemingly call into question the requirement of Sry for brain sexual differentiation.
Sexual differentiation , in human embryology , the process by which the male and female sexual organs develop from neutral embryonic structures. The normal human fetus of either sex has the potential to develop either male or female organs, depending on genetic and hormonal influences. In humans, each egg contains 23 chromosomes , of which 22 are autosomes and 1 is a female sex chromosome the X chromosome. Each sperm also contains 23 chromosomes: 22 autosomes and either one female sex chromosome or one male sex chromosome the Y chromosome. An egg that has been fertilized has a full complement of 46 chromosomes, of which two are sex chromosomes. Therefore, genetic sex of the individual is determined at the time of fertilization ; fertilized eggs containing an XY sex chromosome complement are genetic males, whereas those containing an XX sex chromosome complement are genetic females. Every fetus contains structures that are capable of developing into either male or female genitalia, and, regardless of the complement of sex chromosomes, all developing embryos become feminized unless masculinizing influences come into play at key times during gestation.
Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote. At an early stage in embryonic development, both sexes possess equivalent internal structures.
Ieuan A. Mammalian sex differentiation is a hormone-dependent process in the male following the determination of a testis from the indifferent gonad through a cascade of genetic events. Observations in several human syndromes of disordered fetal sex development corroborate findings in murine embryo studies, although there are exceptions in some gene knockout models. The ubiquitously expressed AR interacts in a ligand-dependent manner with coregulators to control the expression of androgen-responsive genes.