... components.¹

We'll soon see that separating genotypic and environmental components is far from trivial.

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... variance.²

Strictly speaking we should also include a term for the interaction between genotype and environment, but we'll ignore that for the time being.

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... experienced.³

When I put it this way, I hope it's obvious that I'm neglecting genotype-environment interactions, and that I'm oversimplifying quite a bit.

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... genotype,⁴

Don't worry about what I mean by additive genotype--yet. We'll get to it soon enough.

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... genes.⁵

As we'll see later it can do this only for the range of environments in which it was measured.

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... selection.⁶

Or at least only the additive genetic variance responds to natural selection when zygotes are found in Hardy-Weinberg proportions.

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...table:definitions).⁷

Warning! There's a lot of algebra between here and the end. It's unavoidable. You can't possibly understand what additive genetic variance is without it. I'll try to focus on principles, but a lot of the algebra that follows is necessary. Sorry about that.

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... genotype.⁸

Remember. We're now considering traits in which the environment influences the phenotypic expression, so the same genotype can produce different phenotypes, depending on the environment in which it develops.

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... allele.⁹

Hold on. Things get even more interesting from here.

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... proportions.¹⁰

As you should have noticed in Table 1.

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....¹¹

We won't bother with proving that the resulting estimates produce the minimum possible value of $a$. Just take my word for it.

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... population.¹²

If you've been paying close attention and you have a good memory, the expressions for $\alpha_1$ and $\alpha_2$ may look vaguely familiar. They look a lot like the expressions for marginal fitnesses we encountered when studying viability selection.

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