Population genetics of complex traits

My personal website and blog

Recent Posts

Why we expect genetic differences between populations to be zero

We expect the genetic difference between two (or an arbitrary number of) groups that diverged from some common ancestral population to be zero under neutrality. This is a well-known result that I feel like isn’t discussed enough, especially in discussions around mean differences in traits such as IQ and educational attainment.

Last updated on Mar 14, 2021 10 min read main

Heritability (3): Non-additive effects dominance

Dominance is a just a fancy-schmancy way of saying that the phenotypic effects of alleles at a single locus are not additive 💁‍♂️. Ok, but what does that mean?

Arslan A. Zaidi

Oct 24, 2018 5 min read main

What your genetic ancestry test can and cannot tell you about your genealogical ancestors

The topic of this post was not on my radar 📡 but I don’t live under a rock and I’ve been following the recent developments with Elizabeth Warren and her much publicized ancestry results.

Last updated on Nov 19, 2020 6 min read main

Heritability (2): narrow and broad sense heritability

Quick recap: I mentioned last time that heritability = Vg / Vp, where Vg is the genetic variance among individuals and Vp is the total phenotypic difference among individuals. Furthermore, Vp = Vg + Ve, where Ve is the environmental variance contributing to phenotypic differences.

Arslan A. Zaidi

May 4, 2018 4 min read main

Heritability (1): How 'genetic' is a trait?

One of the reasons I’ve come to write about this is because recently I’ve been asked a lot about “how genetic is this trait or that trait?”. And I find myself responding with another question (yeah I’m that guy , get over it): “What do you mean by genetic?

Arslan A. Zaidi

Apr 25, 2018 3 min read main

Derivations

Why does admixture create LD between unlinked loci?

Admixture generates linkage disequilibrium between loci, even those that are unlinked (i.e. segregate independently or reside on different chromosomes). A lot of my PhD was spent thinking about admixture and admixture LD gave me some grief.

Last updated on Oct 9, 2021 8 min read derivation

A general model for the bias in variant effect sizes due to population structure

Motivation The effects of population structure in GWAS (genome-wide association studies) have been well-studied. It’s one of those problems that on a surface level is quite easy to grasp intuitively.

Last updated on Feb 1, 2021 6 min read derivation

Effect size of a tag variant

Motivation Ever wondered why the effect size of a tag variant is \(r\beta_{causal}\)? Here, \(r\) is the correlation (measure of LD) between the tag and causal variant, and \(\beta_{causal}\) is the effect size of the causal variant.

Arslan A. Zaidi

Last updated on Dec 20, 2020 12 min read derivation