Lesson 4: Gene Expression and Personal Traits
The genetics of traits such as PTC tasting or ABO blood group type are fairly easy to explain because they are influenced by single genes with few alleles. They are monogenic traits. Most human traits are complex because they are influenced by multiple genes, some with several alleles. Traits such as eye color and height are polygenic, complex traits. All of the different genes and alleles that contribute to these traits are not yet known. Geneticists are making steady progress toward understanding how polygenic traits are produced.
Genetic diseases and genetic disease susceptibilities that are monogenic can be categorized as dominant, co-dominant, or recessive. For example, Huntington's disease is a monogenic dominant trait. Sickle cell disease is a monogenic co-dominant trait. Cystic fibrosis is a monogenic recessive trait.
Many genetic disease susceptibilities are complex, polygenic traits. Inherited susceptibility to cancer or cardiovascular disease can be monogenic or polygenic. In addition, environmental factors greatly influence the risk of developing some diseases.
