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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All start out female for the first several weeks. It is only later in the pregnancy that hormones are turned on/off to determine gender.
Sexual attraction and sexual identity come later, too. The same bits of tissue in the initially female baby will turn ovary into testicles, the clitoris into a penis, and so on. Or in the absence of those hormones, they remain in the initial female form.
And to make things even more (potentially) confusing, the timing and duration of hormones affecting each of the three variables (sex, identity, and attraction) can occasionally vary from “normal” and you get a person who is gay/lesbian and/or transgender or another combination all together.
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Sex determination happens on different levels.
Chromosome is the fundamental one.
Because Y chromosome has the message (genes) to produce (Testosterone), which is lacking in X chromosome, fetus with XY pair can modify the gonad (which is same for both male and female until 6-7 weeks of life) to a male.
Generally speaking, it is this influence of Testosterone that makes us male. If we can block the effects of testosterone, even a fetus with XY can be a female with Ovaries and vagina as our default development is to be a female.
But, even when there is chromosome, the downstream signal translation requires a lot of different receptors.
when is the assignment due?
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Interesting fact, when they do a blood test on pregnant women, they look for Y chromosomes in the blood to determine if the baby is a boy, because the mother and baby share the same blood.
Short story: whether a Y-chromosome is present or not, and this is delivered by the sperm.
All fetuses in development start out exactly the same-bones, muscles, proto-organs, etc. This is because the X chromosome contains far more genetic information than the Y. If the fetus has two X chromosomes then development will continue as before-developing a uterus, ovaries, wide pelvis, etc and it will become a female.
If a Y-chromosome is present though the same proto-organs will change form. The ovaries drop and develop into testicles. The clitoris develops into a penis with the urethra running along its length rather than terminating near the pelvis. The labia minora stretch and become the scrotum. The hips develop to be narrower and hips more in-line.
>All vertebrate embryos are inherently female anyway, they just require an extra hormone given at the right developmental stage to make them male.
Source: *Jurassic Park*
Ay the moment the sperm cell and egg combine it’s already decided, sperm can have an X or Y chromosome if it’s X it’s female while Y is male
The DNA determines sex. The father either provides an X or a Y chromosome which pairs with an X provided by the mother. XY makes a male, XX makes a female. In the case of a male, the Y chromosome is present which carries a gene on it called SRY, which around 6-8 weeks causes a protein called TDA (testicle determining factor) to be produced. This protein signals the gonads (which at this point could become ovaries or testicles) to become testicles. Then, the testicles will begin to make testosterone which will trigger a bunch of other things to happen that result in a male child. They also make another hormone that blocks female traits from developing. Lacking a Y chromosome, none of these things happen and the child continues to develop as female.
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