An inheritable trait can be:
- Monogenic, if caused by a mutation or alteration in the DNA sequence of a single gene. It is also called Mendelian hereditary trait because it is transmitted according to precise rules, discovered by Mendel. Regarding diseases, more than 6,000 monogenic hereditary diseases are known – even so, they are less than the polygenic ones.
- Polygenic, if caused by mutations or alterations in the sequence of several genes. Polygenic features are very common – for example, fingerprint, height, eye color and skin color. Some of the most frequent chronic diseases are also polygenic, such as hypertension, Alzheimer’s disease, schizophrenia, asthma, diabetes mellitus, various types of cancer and obesity.