This document summarizes several genetics concepts including incomplete dominance, multiple alleles, polygenic inheritance, environmental impacts, mutations, recessive genetic disorders, sex determination, and sex-linked disorders. Incomplete dominance is when neither allele is dominant, resulting in an intermediate phenotype. Multiple alleles control traits through more than two alleles producing more than three phenotypes, such as the four blood types. Polygenic inheritance occurs when multiple gene pairs act together to influence complex traits over a wide range.