... following:¹

If we ignore sampling error.

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... population,²

We'd get the same result by relaxing this assumption, but the algebra gets messier, so why bother?

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... frequencies.³

For example, if we combine samples from different years or across age classes of long-lived organisms, we may see a deficienty of heterozygotes in the sample purely as a result of allele frequency differences across years.

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... populations.⁴

If you're curious about this, feel free to ask, but I'll have to dig out my copy of Li [1] to answer. I don't carry those details around in my head.

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... expected.⁵

And this is what we predicted when we started.

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...$F_{st}$⁶

The reason for the subscript will become apparent later.

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... possible.⁷

I say ``one way'', because there are several other ways to talk about $F_{st}$, too. But we won't talk about them until later.

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... too.⁸

At least it's easy once you've been shown how.

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... sample.⁹

For the time being we're going to assume that we know those frequencies exactly. In real applications, of course, we'll estimate those frequencies from data, so we'll have to account for sampling error when we actually try to estimate these things.

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... before.¹⁰

It takes a fair amount of algebra to show that this definition of $F_{st}$ is equivalent to the one I showed you before, so you'll just have to take my word for it.

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