In each egg and sperm, there are millions of possible combinations of genes. That means that there are trillions of combinations that could result! This combination of genes creates an individual with genes in an order that has never happen before and will never occur again. With the exception of identical twins, no two people are ever alike. To put it into perspective, a person in the United States has approximately a 1 in 700,000 chance of getting struck by lightning in any given year. That means you would have a better chance of getting struck by lightning millions of times in one year then guessing an exact combination of genes.
Source: Genetics a Living BluePrint