Sex determination in embryos is a complex process involving genetic and molecular events that guide sexual differentiation. In mammals, including humans, sex is primarily determined by sex chromosomes: females inherit two X chromosomes (XX), while males inherit one X and one Y chromosome (XY). The sperm's chromosome (X or Y) determines the embryo's chromosomal sex.
The SRY (Sex-determining Region Y) gene, located on the Y chromosome, plays a crucial role in male sex determination. It acts as a master switch, initiating a cascade of molecular signals early in embryonic development. This gene stimulates the formation of precursor cells that differentiate into testes. Without the SRY gene, the embryo defaults to female development, forming ovaries.
During early gestation, the embryo possesses both ovarian and testicular precursor cells. Activation of the SRY gene triggers changes in gene expression and tissue organization, leading to testes formation in male embryos. Other genetic and epigenetic factors also contribute to this process, ensuring proper development of gonads and secondary reproductive organs.
While mammals rely on the SRY gene for sex determination, other organisms exhibit diverse mechanisms. Some reptiles use environmental temperature, while birds and insects employ different genetic systems like the ZW system.
Understanding embryonic sex determination has implications for diagnosing and treating disorders of sexual development, advancing reproductive biology, and conducting research in genetics and epigenetics. Studying the SRY gene and related mechanisms offers insights into the interplay between genetics, environment, and development.