polygenic inheritance

Polygenic inheritance is when a single trait is shaped by many genes pulling together, like an orchestra where no one instrument carries the melody — the sound is the sum of many small parts. Each contributing gene adds or subtracts a little from the outcome, and the trait you observe reflects their combined performance rather than any single soloist.

Because the contributions stack additively, the more genes involved and the more evenly their effects are spread, the smoother the resulting range of phenotypes becomes. Cross two parents who differ at many such genes and the offspring distribution fills in the whole spectrum between them. This is the genetic engine behind continuous variation and most quantitative traits, and it is exactly what makes those traits hard to trace back to any one piece of DNA.

Polygenic inheritance still obeys Mendel's rules at each individual locus — alleles segregate and assort as usual. What changes is that you can no longer read the phenotype off a simple genotype, because so many loci act at once and environmental noise blurs the picture further. Counting categories gives way to measuring distributions.