Is there variability in genetic combination from the same sperm and egg combination
Assuming we know the haplotype of the ovule and the haplotype of the spermatozoid, then the genotype of the future egg is perfectly deterministic. This is true to the extend that none of the following rare events occur:


mitochondria could be inherited from the father as well
mutations in the broad sense (see here for definitions) may occur outside an event of mitosis or meiosis
The egg might pick up random sequence floating in the environment


Of course epigenetics elements might vary but this is another discussion.