First, all biologists everywhere are still obsessed with "one gene" answers. Even when they use big-data tools, they use them to come up with lists of genes, each of which they say has a measurable independent contribution to whatever it is they're studying. This is looking for your keys under the lamppost. The effect of one gene allele depends on what alleles of other genes are present. But try to find anything in the literature acknowledging that. (Admittedly we have probably evolved for high independence of genes, so that we can reproduce thru sex.)

? I see mentions of stuff like dominance and interaction all the time; the reason people tend to ignore it in practice seems to be that the techniques which assume additive/independence work pretty well and explain a lot of the heritability. For example, height the other day: "Defining the role of common variation in the genomic and biological architecture of adult human height"

Using genome-wide data from 253,288 individuals, we identified 697 variants at genome-wide significance that together explained one-fifth of the heritability for adult height. By testing different numbers of variants in independent studies, we show that the most strongly associated ~2,000, ~3,700 and ~9,500 SNPs explained ~21%, ~24% and ~29% of phenotypic variance. Furthermore, all common variants together captured 60% of heritability.

Seems like an excellent start to me.