Is gender heritable

Gender is determined by the sex chromosome pair which in a woman is designated to be (XX) and in a man (XY).

A baby is made with 1/2 each pair of chromosomes coming from the man (in the sperm) and 1/2 coming from the woman (in the egg).

Thus regarding the sex chromosome pair, the woman will always contribute an (X) in her egg and each of the man's sperm will contain either an (X) or a (Y) chromosome (sperm containing (X) or (Y) are produced in equal amounts).

Therefore while gender is inherited from the man, it is purely a matter of chance as to weather a sperm with an (X) or a (Y) chromosome reaches the egg first. This means that 1/2 the population should be men and 1/2 should be women. However the (Y) chromosome is shorter and smaller than the (X) and this makes a (Y) sperm slightly lighter and therefore able to swim slightly faster than an (X) sperm. Thus looking across all human population, naturally slightly more men are produced than women - (105 boys to 100 girls).