Types of Genetic Traits

Sometimes, having one single copy of a gene results in a disease or trait. We call this a dominant genetic model. For example, someone with a single risk allele for Huntington’s disease will develop the condition.

Some diseases or traits only occur if you have 2 copies of a gene. We call this a recessive genetic model. Sickle cell anemia is one example.

Most of us learned about dominant and recessive genetic models in high school biology class. However, it turns out that they are rare.

The majority of traits are the result of a lot of genes. These genes work in an additive manner.

Human height follows an additive model. For each gene that influences height, two copies of the “tall” allele add twice as much total height as only one copy. There are also a lot of genes that influence height. Most alleles/variants work this way.