Is a first cousin as much kin to me as my half sister?

Question:

Is a first cousin as much kin to me as my half sister?

Best Answer - Chosen by Asker: Depends on how you define "as much kin", but I would say not quite: your half sister has half her genes from the exact same person as you got half your genes from, whereas you have to go back to a grandparent to find such a common "donor" with your first cousin.

Let's do this sort of mathematically. Let G and H be your grandparents, and let P and Q be their children (your parent is P, your cousin's is Q). Unless they're identical twins (in which case your cousin would be as much kin as your half sister), they're each a different "crossing" of G's and H's genes: P = (G x H)1, Q = (G x H)2. Now let L, M, and N be the other parents of your generation:

You = L x (G x H)1
Half-sis = M x (G x H)1
Cousin = N x (G x H)2

Because it's theoretically possible for siblings not to share any genes, those numbers after (GxH) are important (in my opinion) in determining degree of kinship.