In a developing fetus, what influences whether it is going to become male or female? What influences the cells to start building male or female organs?
Wait. This question is put very wrong in the beginning. In a developing fetus, the sex is defined already. It’s defined by the sex chromosome that the sperm brings into the egg. The mix of genes that are read off two X chromosomes will trigger a female development, while the XY chromosome combination does not reach enough “female gene products” and adds a lot of “male” hormones, which will ultimately trigger development of male sexual organs. It’s worth to know that it’s more the “not enough female” that triggers male development, rather than “not enough male” triggering female development. The Y chromosome that male are so proud of (talking about all these patriarchy in the world) is evolutionary a crippled X chromosome. 🙂
Hormones and chemical gradients.
Remember that whichever sperm fertilized the egg already decided the genetic profile wherever there’s an X or Y chromosome.
The SRY gene specifically regulates male vs female and helps activate other genes.
If you go by the available chromosomes, your sex is predetermined, as in, what you will be by the time you’re born.
But, functionally, it takes about 6 weeks before we develop into a male if there’s a y chromosome around. The y chromosome comes from the sperm.
Side fact: Because the sperm carries the y chromosome, a male can be cloned into a female version, but a female can’t be cloned into a male version.
as an embryo is developing, there will eventually be a “check” for a specific gene on the Y chromosome called the SRY gene. this occurs around the 6th week of pregnancy, and it acts as the trigger for a whole bunch of other genes to activate and start developing the male sex organs, while also suppressing the development of female sex organs. if the SRY gene is absent (like in typical females, no Y chromosome = no SRY), or defective (someone with XY but the SRY gene doesn’t work for some reason), the embryo will go on to develop as a female. this is why you might have heard the factoid that we all start off as females during development.
It’s predetermined by the chromosomes in the sperm cell.
The egg cell is always X. The sperm cell will be either X or Y.
When combined, the cells become either XX (female) or XY (male) and thus the cells continue to grow into a male or female human.
Two halves to make a whole 🙂