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?
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The SRY gene (a gene that is typically on the Y chromosome in most mammals, though can rarely be on the X as well and can be absent from the Y chromosome) causes the development of Leydig cells of the testis which start secreting testosterone and the development of Sertoli cells which produce anti-Müllerian hormone.
Testosterone can be transformed into DHT by alpha-5 reductase. Testosterone and DHT cause the development of male organs.
The anti-Mullerian hormone causes the non-development of female organs.
The default is the development of female organs. Those hormones change it by getting inside the nucleus and changing how genes are expressed.
Non-mammals have a SOX (SRY-like box) gene that does the same function. This gene can be chromosome-specific or depend on environmental factors like temperature.
That is the presence or absence of the Sex-determining region Y protein (SRY), which is typically found in the Y-chromosome. Hence the X and Y theory, that XX is female, XY is male, but that theory is outdated.
The SRY gene can be absent or inactive in the Y chromosome or be present in the X-chromosome. So you can be XX chromosome and still develop male reproduction organs or XY and develop female reproduction organs. Or you can be XXY.
Sperm determines if a fetus will be male or female. The father determines the gender of the baby. Eggs are always X chromosome while Sperm can be X or Y.
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.
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.
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.
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. 🙂
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 🙂
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