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GeriatricHydralisk t1_jb09yqx wrote

The key is that heritability is statistical, especially with a big population.

Imagine a trait like height, which is continuous and polygenic. Very tall people and very short people (absent any endocrine or developmental pathology) will mostly have alleles for tall and short, respectively, while average height people will have a mix. If your parents are very tall and very short, you'll get alleles from both sides and likely wind up average. Conversely, if your parents are both average, there's a slim chance you could inherit mostly tall or short alleles, but chances are you'll be average. If both parents are at a height extreme, though, variability is lower.

So to estimate heritability, you regress your height against the average of your parents' heights. With enough people, you get a cloud of points that looks like a football at an angle - sloped, mostly points in the middle, and the middle points are further away from the regression axis than either end.

The instances you're interested in are those in the middle of the graph, far off the axis. And they do exist, but, statistically are balanced out by the ones on the other side of the axis. I'm sure there's more math to be done, but that's where my expertise ends.

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SerialStateLineXer t1_jb0xois wrote

>So to estimate heritability, you regress your height against the average of your parents' heights.

No, you can't estimate heritability that way, because this can't distinguish between genetic and environmental transmission of traits.

Traditionally, heritability is estimated with twin studies, using Falconer's formula. You compare the correlation between pairs of monozygotic twins to the correlation between pairs of same-sex dizygotic twins. You can exploit the fact that MZ twins are twice as genetically similar as DZ twins but MZ and DZ twins are raised in equally similar environments to determine heritability.

So if the MZ correlation is 0.7 and the DZ correlation is 0.4, this implies that 60% (2 * (0.7 - 0.4)) of the variation in the trait can be attributed to genetics, 30% (1.0 - 0.7) to non-shared environment (environmental factors that differ between twins) and the remaining 10% to shared environment (environmental factors that are the same for both twins).

There are some additional adjustments you can do for things like gene-environment correlation, but that's the simplified version.

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Georgie___Best t1_jb4u7v7 wrote

>No, you can't estimate heritability that way, because this can't distinguish between genetic and environmental transmission of traits.

What do you mean by environmental transmission of traits?

Parent-offspring regression is definitely one way to estimate heritability. It has flaws and biases, but no more than estimates derived from twin-studies, which tend to overestimate narrow-sense heritability.

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SerialStateLineXer t1_jb5l8n8 wrote

Are you under the impression that heritability of height is defined as the correlation between children's heights and the average of their parents' heights? Obviously you can determine that by calculating said correlation, but that's not what heritability means.

Heritability refers specifically to share of variation in a trait attributable to genetic variation. I suppose it's possible that there's some field other than genetics in which the term is used to refer to the degree to which children are similar to their parents, but the original question specifically referred to the definition used in genetics, and you definitely can't calculate that by comparing children to their parents. If you could, twin studies would never have been invented. That's the exact problem they were invented to solve.

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Georgie___Best t1_jb65yb6 wrote

Somewhat surprised that you're familiar with the concept of heritability, but not yet come across regression of offspring on mid-parents as a method to estimate it. For example:

Parent-offspring regression to estimate the heritability of an HIV-1 trait in a realistic setup

Comparing parent–offspring regression with frequentist and Bayesian animal models to estimate heritability in wild populations: a simulation study for Gaussian and binary traits

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