HUMAN SKIN COLOR A POLYGENIC TRAIT Presented by

HUMAN SKIN COLOR A POLYGENIC TRAIT Presented by Steven Agelidis Biology 108

Polygenic Trait (multiple gene): Ø Human skin color is an example of a polygenic trait. Ø It is known that at least three or four genes control skin color, and for each of those genes, dark pigment has incomplete dominance over light. Ø Someone who is AABBCC would have very dark skin. Ø Someone who is aabbcc would have very light skin. Ø If they would get married and have children, their children would all have Aa. Bb. Cc medium dark skin. Ø If two of those people would get married and have children, the Punnett square would look like this:

Medium dark MALE X FEMALE Medium dark Aa. Bb. Cc

Aa. Bb. Cc X Aa. Bb. Cc Gametes ABC Abc Ab. C Abc a. BC a. Bc ab. C abc ABC AABBCC AABb. Cc AABb. CC AABb. Cc Aa. BBCC Aa. BBCc Aa. Bb. CC Aa. Bb. Cc Abc AABb. Cc AAbbcc AAbb. Cc AAbbcc Aa. Bb. Cc Aa. Bbcc Aabb. Cc Aabbcc Ab. C AABb. CC AAbb. Cc AAbb. CC AAbb. Cc Aa. Bb. CC Aa. Bb. Cc Aabb. CC Aabb. Cc Abc AABb. Cc AAbbcc AAbb. Cc AAbbcc Aa. Bb. Cc Aa. Bbcc Aabb. Cc Aabbcc a. BC Aa. BBCC Aa. Bb. Cc Aa. Bb. CC Aa. Bb. Cc aa. BBCC aa. BBCc aa. Bb. CC aa. Bb. Cc a. Bc Aa. BBCc Aa. Bbcc Aa. Bb. Cc Aa. Bbcc aa. BBCc aa. BBcc aa. Bb. Cc aa. Bbcc ab. C Aa. Bb. CC Aabb. Cc Aabb. CC Aabb. Cc aa. Bb. CC aa. Bb. Cc aabb. CC aabb. Cc abc Aa. Bb. Cc Aabbcc Aabb. Cc Aabbcc aa. Bb. Cc aa. Bbcc aabb. Cc aabbcc

Polygenic Pigmentation Gametes ABC ABc Ab. C Abc a. BC a. Bc ab. C abc

Phenotype Distribution Ø Parental Genotypes Aa. Bb. Cc X Aa. Bb. Cc Dark skin = ABC = Light skin = abc = Ø Offspring Phenotype distribution probabilities: 1/64 very dark 6/64 15/64 20/64 medium dark 15/64 6/64 1/64 very light