Mendelian inheritance refers to patterns of inheritance that are characteristic of organisms that reproduce sexually. The Austrian monk Gregor Mendel performed thousands of crosses with garden peas at his monastery during the middle of the 19th century. Mendel explained his results by describing two laws of inheritance that introduced the idea of dominant and recessive genes.


Mendelian inheritance refers to the kind of inheritance you can understand more simply as the consequence of a single gene. So in human genetics, for instance, when you look at a condition like Huntington's disease, and you see that it follows this pattern where an affected person who passes that to a child, the child has a 50 percent chance of being infected... That's dominant Mendelian inheritance. Hemophilia, where you see a condition where the female seems to be unaffected but there's X-linked inheritance, that's also Mendelian. Or cystic fibrosis, where it's autosomal recessive, you can model that also by Mendel's rules of the consequence of a single gene.

- Francis S. Collins, M.D., Ph.D.