A brief summary of work covered so far in the topic Inheritance and Variation.

Lakshmi Mehta M.D at Mount Sinai Medical Center discusses the roles of recessive and dominant genes.

Hirchsprung’s disease is an abnormality in which certain nerve fibers are absent in segments of the bowel. This disease is caused by certain nerve cells in the large intestine that didn’t develop before birth. Without the nerves, the affected colon lacks the ability to move bowel contents. This disease can affect varying lengths of the bowel segment.

Hemochromatosis is a genetic disorder that causes the body to increase the absorption of intestinal iron. This iron overload can eventually cause cirrhosis of the liver.

Fragile X Syndrome is the most common form of inherited mental retardation. This syndrome is caused by a mutation in the FMR-1 gene on the x chromosome. Individuals with this disorder have developmental delay, variable levels of retardation, behavioral and emotional difficulties, and possible physical traits.