At what stage is a person's sex determined?

[nparker]

At what stage is the sex of a person determined?
single cell. embryo, birth?

[wijey]

Embryo stage. Apparently we are all female initially!

[eram]

When a human egg is fertilized with sperm, the sex of the baby is determined immediately. A women's egg cells and a man's sperm cells each contain 23 single chromosomes, which are not paired until they meet their opposite number. Of the 23 single chromosomes, one is always a sex chromosome. Each egg always has an X (female) sex chromosome, but the sex chromosome present in any sperm can be either X (female) or Y (male). The sex of the baby is dependent on which type of sperm cell fertilizes the egg.

[Matthew82]

A human being's sex is determined by the 23rd pair of chromosomes, the so called X and Y chromosomes. The sex cells (ovum and sperm) each posses only one of each pair of chromosomes, and therefore each contribute half the DNA to the eventual embryo. The sperm cell can possess either an X or Y chromosome, whereas the ovum can only possess an X chromosome. Therefore, offspring either possess XX (and therefore are female) or XY (and therefore are male). So in fact the sex of a person is determined when the sperm cell, which will eventually fertilise the egg, is synthesised.