what is the difference between QTL heritability and heritability?

Question

[Emy]

Hello

I have a question. what is the difference between QTL heritability and heritability?

When is it these events happen?

QTL heritability > heritability

QTL heritability < heritability

QTL heritability = heritability

Regards

Answer 1

[Asaf]

Broadly speaking, narrow sense heritability, h^2, is the percentage of the trait variance explained by genetic factors (additively). SNP heritability or ChIP heritability or QTL heritability is the same as above, only here it is limited by the genetic factors that we can observe using our methods. It is usually the same but I assume there are cases in which we simply cannot observe all the differences in the genome between two groups.

Another term is the broad sense of heritability (H^2) which makes things more complicated. This heritability is the percentage of variation explained by all genetic factors, not necessarily genomic. There are other factors such as epigenetics, gene-gene interactions (which makes the effects not additive, very common in fact) etc. This heritability is larger than narrow sense heritability (or equals to it). It is hard to estimate either of the terms and usually debatable as for which sense of heritability was actually estimated.

[Emy]

Thanks Asaf, I want to add some info that I read is that when qtlh2 < h2 means we have polygenic (infinitesimal) effects [both polygenic and QTL effects] in our population.

Do you agree with this idea?

[Asaf]

It basically mean that there are QTL with an effect too small for us to discover. So theoretically we should be able to explain h2 with QTLs but it's limited by our methods (sample size, sequencing etc.)