Quote Originally Posted by asplundii View Post
Any given offspring shares 50% of its parents genes.

Any two siblings share 50% of their genes.

So parent x offspring = sib x sib
This is not exactly correct. Lets do the math. Lets say you have 2 snakes with 2 alleles each allele having 2 genes and you breed them together and get 2 offspring.

Dad has 4 genes in 2 pairs. AB and CD Mom has 4 genes in 2 pairs EF and GH.

So your combos for offspring are
AE and CG
AE and CH
AE and DG
AE and DH
AF and CG
AF and CH
AF and DG
AF and DH
BE and CG
BE and CH
BE and DG
BE and DH
BF and CG
BF and CH
BF and DG
BF and DH

Ok so the point is that its possible to get two siblings that have no genes in common. (AE and CG) and (BF and DH) for instance.

So parent x offspring = 50% shared genes
and sib x sib ≈ 50% shared genes

For those of you not math nerds the wavy equal sign means approximately.
Statistically siblings share 50% of their genes when looked at in total. They can and will have alleles that are identical and some that are completely different. With a parent x offspring pairing you get 50% shared per allele and thus 50% total.