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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In mammals, egg cells from females contain an X chromosome, and sperm cell from males have either an X or Y chromosome. When they come together, the result is a cell that has either XX or XY (usually). That cell keeps dividing and develops into the baby.
There’s a gene called SRY that’s usually on the Y chromosome. It causes cells to make a protein that grabs onto DNA in a way that turns on a series of other genes that trigger modifications to anatomy that turn the animal male. The most important gene it turns on in the process is called “testis determining factor”, and that signals cells making sex organs to switch to the male pattern. It’s quite complicated, but flipping that one switch changes hormones and genetic activity that alter the development of the embryo.
Because SRY is on the Y chromosome, animals that have two X chromosomes are usually female, and those with an X and Y are usually
male. There are instances where the SRY gene breaks off and becomes part of an X chromosome, which gives us XX males. Also sometimes there are mutations in the SRY gene or other genes it interacts with so it doesn’t work and you get XY females (or intersex individuals).
Interestingly, precisely what genes SRY turns on differs among mammals.
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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?
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.
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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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