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## Inbreeding effective size

You may also remember that we can think of genetic drift as analogous to inbreeding. The probability of identity by descent within populations changes in a predictable way in relation to population size, namely

So another way we can make our actual population equivalent to an ideal population is to make them equivalent with respect to how changes from generation to generation. We do this by calculating how the inbreeding coefficient changes from one generation to the next in our actual population, figuring out what size an ideal population would have to be to show the same change between generations, and pretending that our actual population is the same size at the ideal one. So suppose and are the actual inbreeding coefficients we'd have in our population at generation and , respectively. Then

In many applications it's convenient to assume that . In that case the calculation gets a lot simpler:

We also don't lose anything by doing so, because depends only on how much changes from one generation to the next, not on its actual magnitude.

Next: Comments on effective population Up: Effective population size Previous: Variance effective size
Kent Holsinger 2012-09-23