I have put scalloped potatoes and ham into the oven and have a few minutes free, so:
The degree of inbreeding for a particular pairing (the inbreeding coefficient of that mating) represents the degree of shared genes by common descent. (You can ignore the 'by common descent' part of that phrase unless you are a geneticist or lawyer, but it does mean that inbreeding coefficient is not necessarily quite the same as % shared genes).
Think of it this way: half of your genes are from your mum, half from your dad, right? Same is true of your brother/sister.
If you were to compare a list of the genes (really should say "alleles" but I'll use the common usage) that you carry vs a list of the genes that your dad carries, half of the genes you have will be present on your dad's list.
If you were to compare a list of the genes that you carry vs a list of the genes that your sibling carries, it's the same -- half the genes that you have, your sibling has also. It'll just be different entries in the list that are shared (as compared to the particular ones shared in the previous example).
(The reason the inbreeding coefficient = 0.25 for both matings whereas my conversational description involves one half is: math <g>. If you like sigmas and n's and exponents, you can look it up
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It gets more complicated once you get past the first generation because the parents of subsequent generations are themselves somewhat inbred (share some genes by common descent).
One really really big advantage of parent-offspring matings In Real Life Animal Breeding, as compared to sib-sib breedings, is that the parent has had time to a) be carefully selected on the basis of traits shown as a mature individual, and b) be progeny-tested with individuals throwing suspicious/poor progeny being discarded from the breeding program. So one of the two parties is an older 'known quantity', whereas in sib-sib matings that is generally not the case. There can be other considerations as well.
I don't know if that helps any?
Pat, heading back to the kitchen
