Random Fertilization
 

Fertilization is a random event with many possible outcomes. To determine the probability that any one sperm will fertilized any particular egg, you multiply the probability of the separate events together.

That is, 1 in over 8 million  X 1 in over 8 million, which is a number greater that 1 in over 64 trillion.

Any fertilized egg possesses a combination of genes, that is one in over 64 trillion different possible combinations.