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?

In: 274

Answer 1

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.