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?

Question

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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Answer 1

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.