Explain why polygenic traits are expressed through quantitative variation, using skin color as an example.

If there are more alleles present for darker skin tone, then the offspring will have darker skin pigment than the parents may have.

There can be varying expressions of pigment color from dark to light based on the alleles received, even in the same family.

The sum of the allele combinations determines the expression of the trait from one degree to the other.

A bell curve shows the quantitative variation.

Polygenic traits are quantitative because their phenotype expression depends on several different alleles found on different chromosomes.

Explanation:

In this case each dominant capital gene produces one unit of skin color, therefore, a wide range of intermediate skin colors are produced depending on the number of dominant capital genes.