Coin flipping simulates the events of mitosis and the production of sperm or eggs

Coin flipping simulates the events of mitosis and the production of sperm. This is because females carry XX chromosomes so all eggs will have a singular X chromosome. It is the sperm that determines the sex of the foetus: males have XY chromosomes and therefore sperm will carry either X or Y chromosomes (a 50/50 chance, just like flipping a coin)