Developmental Biology. This new knowledge shows that the inherent inequality of X and Y genetic material in the two sexes has effects throughout the body, not just on the gonads. In some cases, they do, but their relative magnitude can be altered by gonadal hormones. In mammals and birds, sex differences originate in the genome, at the time of conception.
Figure 7. Biochem Biophys Res Commun : — The early stages of human differentiation appear to be quite similar to the same biological processes in other mammals and the interaction of genes, hormones and body structures is fairly well understood.
Compelling evidence for the role of coregulators in hormone action comes from studies in SRC-1 mutant mice Volume This article has been cited by other articles in PMC. Graves Search ADS. The pentagon tip points to the relative gene orientation.
In humans, biological sex is determined by five factors present at birth: the presence or absence of a Y chromosome, the type of gonadsthe sex hormonesthe internal genitalia such as the uterus in femalesand the external genitalia. New York: Penguin. Current theories on mechanisms of sexual differentiation of brains and behavior in humans are based primarily on three sources of evidence: animal research involving manipulation of hormones in early life, observation of outcomes of small numbers of individuals with intersex sex determination and sex differentiation in language in Wisconsin or cases of early sex reassignmentand statistical distribution of traits in populations e.
Thelarche Development Lactation Breastfeeding.
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.
The differential representation of X and Y genetic material is the sole source of all subsequent sex differences during development and adulthood, because all other factors autosomal genes, cytoplasmic material, prenatal environment of the zygote are thought to be equivalent, on average, between males and female zygotes.
That method, however, raises questions whether the sex chromosome effects also occur when hormones are present. First synthesis of testosterone.