Most disease-causing gene mutations are uncommon in the general population. However, other genetic changes occur more frequently. Genetic alterations that occur in more than 1 percent of the population are called polymorphisms. read more
For the gene to spread through the population, it could just be that a virus affects a lot of them, or it could be that the mutant gene is beneficial and is selected for, or it could be that the mutant gene is neutral but it happened to first occur in a line which was especially fertile for other reasons. read more
A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. Mutations range in size; they can affect anywhere from a single DNA building block (base pair) to a large segment of a chromosome that includes multiple genes. read more