On average, each person has approximately 100 to 400 genes with variations or mutations (with different genes being affected in different individuals). However, in most cases, the matching gene on the other chromosome in the pair is normal, which helps prevent potential negative effects. In the general population, the likelihood of an individual inheriting two copies of the same abnormal gene—and thus developing a genetic disorder—is very low. However, this risk increases significantly for children of parents who are closely related by blood.