Answer;
Polygenic traits are quantitative because their phenotype expression depends on several different alleles found on different chromosomes.
Step-by-step explanation;
-Using human skin color as an example of polygenic inheritance.
-If we assume that three dominant capital letter genes (A, B and C) control dark pigmentation because more melanin is produced. The recessive alleles of these three genes (a, b & c) control light pigmentation because lower amounts of melanin are produced.
-A genotype with all dominant capital genes (AABBCC) has the maximum amount of melanin and very dark skin. A genotype with all recessive small case genes (aabbcc) has the lowest amount of melanin and very light skin.
-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.