How Is Sex Determined?

  • By Rick Groleau
  • Posted 10.20.01
  • NOVA

The sex of an egg cell is set as soon as it is fertilized, but what happens to that cell and the cells it divides into to make a baby boy or a baby girl? In this step-thru, see how gonads—which look identical in early-stage embryos—become either testes or ovaries.

Launch Interactive Printable Version

See how a human embryo develops the key characteristics that make it male or female.

This feature originally appeared on the site for the NOVA program Sex: Unknown.

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