fundamentals
Genes and Chromosomes
Genetic Disorders
People carry an average of 100 to 400 abnormal genes. A genetic disorder is a detrimental trait caused by an abnormal gene. The abnormal gene may be inherited or may arise spontaneously as a result of a new mutation. Gene abnormalities are fairly common. Every human carries an average of 100 to 400 abnormal genes (different ones in different people). However, most of the time the corresponding gene on the other chromosome in the pair is normal and prevents any harmful effects. In the general population, the chance of a person having two copies of the same abnormal gene (and hence a disorder) is very small. However, in children who are offspring of close blood relatives, the chances are higher. Chances are also higher among children of parents who have married within an isolated population, such as within the Amish or Mennonite communities. 