Medical genetics is the study of human genetic variation of medical significance. It is a multi-dimensional discipline that encompasses elements from molecular, cellular, organismal, and population biologies. Although once thought to be a relatively esoteric science, genetics now plays a key role in essentially all subspecialties of medicine. It has been suggested that, with the exception of trauma, genetics may be the underlying cause of all medical complaints. herefore, when a gene that causes a particular disease is identified, it becomes important to understand the inheritance and expression of that gene.

The era of medical genetics was born when Archibold Garrod identified the first genetic diseases, the inborn errors of metabolism. Over the years, other similar disorders have been identified and were shown to be caused by defects, or mutations, in particular biochemical pathways. Examples include phenylketonuria (PKU), Tay Sachs disease, hypercholesterolemia, cystic fibrosis, and galactosemia...