Standard models in population genetics look up at the evolution of few loci which impact fitness. The variance in fitness is determined by the genetic variance and the environmental variance (and the co-variance between environment and genetics). In this question I am interested only about genetic variance and about what percentage of the total genetic variance in fitness do $n$ loci explain.
The question is:
In general, in natural populations, what percentage of the total genetic variance is explained by the $n$ most important loci? Here, by "most important loci" I mean loci which variance explain much of the total genetic variance.
In other words, the subquestions are of the kind:
- how much of the fitness variance does the most important locus explain?
- How much of the fitness variance do the 3 most important loci explain?
- How much of the fitness variance do the 100 most important loci explain? … or if you prefer…
It is obvious that the answer depends on the population under consideration. Factors that might influence the answers are for example
- population size
- environment stability
Beside this question, I also welcome some insights concerning how different factors are likely to influence the answer.
After @SYK's answer, I want to make sure that you understand what definition "genetic variance" I am implicitly using...
Implicitly, I meant the following definition: $V_G = H \cdot V_P$, that is the genetic variance is equal to the heritability times the phenotype variance. For, example one could consider one continuous phenotypic trait and measure its variance in a given population ($V_P$). One can then calculate the heritability (in the narrow sense) by calculating for example a regression of the mean (in case of sexual reproduction) parents phenotypes on the offspring phenotypes, where the slope of the regression is the heritability in the narrow sense ($H_N$). From these $V_P$ and $H_N$, one can calculate the (additive) genetic variance.