By the end of this section, you will be able to:

Explain the basic principles of the theory of evolution by natural selection
Describe the differences between genotype and phenotype
Discuss how gene-environment interactions are critical for expression of physical and psychological characteristics

This lesson will explain that genotypes can be either homozygous or heterozygous. It is 1 of 4 in the series titled "Types of Traits." [2:15]