Dominant & Recessive
What do peas have to do with human health?
So far, we've talked about Mendelian inheritance in terms of traits like pea color and eye color. However, Mendelian inheritance also governs the transmission of many less desirable qualities, such as diseases. We refer to these diseases, appropriately, as "Mendelian diseases." Mendelian diseases can be recessive (examples include Tay-Sachs disease and cystic fibrosis) or dominant (examples include Huntington's disease and Marfan syndrome).
Although there are many Mendelian traits, most traits are not actually controlled by a single gene. Instead, many different genes contribute to the final phenotype. We refer to these traits as "polygenic" (i.e. "multiple genes"). For example, skin tone and susceptibility to heart disease are polygenic. In the next section, we will discuss principles applicable to the study of these kinds of traits, which necessitate more advanced computational skills and tools.
In the next lesson, we'll talk about height and weight, two such polygenic traits. Continue on to learn more!