The sex of a human embryo is determined at the moment of fertilization by the combination of sex chromosomes from the sperm and egg. An embryo with XX chromosomes will develop as female, while an embryo with XY chromosomes will develop as male. Although the genetic sex is established at conception, the physical development of male or female characteristics does not begin immediately.
Prior to the seventh week of pregnancy, the embryo is considered sexually indifferent, meaning it possesses the potential to develop into either sex. Both male and female embryos start with similar, undifferentiated reproductive structures, including a combined clitoral-penile tubercle and precursors to both male and female internal organs. This initial stage is often described as a "default" female development pathway because, in the absence of specific male-determining signals, the embryo will naturally develop female characteristics.
The key event that triggers male development is the activation of the SRY gene on the Y chromosome, which typically occurs around the sixth week of gestation. This gene initiates the development of testes, which then produce androgens like testosterone and anti-Müllerian hormone (AMH). These hormones suppress the development of female structures and promote the formation of male genitalia. Without the SRY gene and the subsequent production of these hormones, the embryo will follow the female developmental pathway, leading to the formation of ovaries, the Müllerian ducts, and female external genitalia.
Therefore, while the genetic sex is determined at fertilization, the physical manifestation of sex is not apparent until around the seventh week of pregnancy, when hormonal signals begin to differentiate the embryo into male or female. The idea that all embryos start as female is a simplification of the biological process, reflecting the fact that female development proceeds without the need for additional male-specific signals, whereas male development requires the activation of specific genes and hormones.
I would like an environmental study to see if temperature, alcohol , drugs , testosterone has anything to do with the sex of a child
