In this activity, students extend the concepts covered in the short film The Biology of Skin Color through the application of models and mathematical thinking to explain how genomic variation and human ancestry can explain differences in skin color, a polygenic trait.

Humans living in different parts of the world have different natural skin colors. In this three-part activity, students learn how patterns in variations in several genes provide an explanation for differences in this trait. In Part 1 of this activity, a simple mathematical model illustrates an idealized relationship between the number of genes involved in a trait and the number of phenotypes that can occur from the combination of alleles. In Part 2, students learn about the methods geneticists use to identify skin color genes and to estimate heritability. Finally, in Part 3, students learn how geneticists analyze genetic variations to trace an individual’s ancestry. They then draw conclusions about the predominant ancestry of two different individuals by comparing their genetic profiles against real allele frequency data.