Where do the Faulty Genes Come from?

A child inherits one of each pair of chromosomes (and one of each pair of the genes they contain) from each parent. At times, a disease or defect can occur if only one parent passes along the gene for that disease (even though the child receives a normal gene from the other parent). This is called dominant inheritance and includes birth defects such as achondroplasia (a form of dwarfism) and Marfan syndrome (a disorder characterized by abnormally long fingers, arms, and legs).

Some birth defects happen only when both healthy parents pass along a faulty gene for the same disease to the child. This is called recessive inheritance and comprises conditions such as Tay-Sachs disease or cystic fibrosis.

  To cap it all, some boys inherit disorders from genes passed on to them by their mothers. These defects, which include conditions such as hemophilia and color-blindness, are called X-linked because the genes are carried on the X chromosome. Since males have only the one X chromosome they receive from their mothers (females have two X chromosomes - one from each parent), a faulty gene on the X chromosome they obtain will cause a problem because they don't have a normal copy of the gene on the other X chromosome that females have.

The quantity or structure of chromosomes can also provoke birth defects. A fault during the formation of an egg or sperm can be a reason of birth a baby with too few or too many chromosomes or with a damaged chromosome. Such birth defects caused by chromosome problems contain Down syndrome. The threat of this type of birth defect often rises with the age of the mother.

Environmental causes of birth defects have connection with the mother's health and influence upon chemicals or diseases. When a mother has definite infections (such as rubella) during pregnancy, it can cause birth defects. Alcohol abusive mothers can be a reason of fetal alcohol syndrome to their posterity, and certain medications taken by the mother can cause birth defects.