Chapter 25 : Human Molecular Genetics

Abstract:

This activity extends the discussion of the molecular basis of genetics to human beings. The background information for students focuses on specific single-gene disorders and on the difficulties of studying genetics in humans. The activity discusses the molecular genetics of cancer. The characteristics of genetic diseases vary widely, depending on the type of change and the gene in which it occurs. Genetic diseases can be divided into three categories: chromosomal defects, single-gene disorders, and multigenic traits. Chromosomal defects include missing or extra chromosomes and rearrangement or deletion of parts of chromosomes. Chromosomal disorders include gain or loss of an entire chromosome (aneuploidy), loss of part of one or more chromosomes (deletion), transfer of one segment of a chromosome to another chromosome (translocation), and reversal of a segment of a chromosome (inversion). The best-known chromosomal disease is probably Down syndrome, caused by an extra copy of chromosome 21. A chromosomal disorder involving the sex chromosomes is Klinefelter’s syndrome. Translocations and deletions can give valuable clues to the locations and functions of particular genes. Multigene disorders including familial hypercholesterolemia, Huntington’s disease (HD) and cystic fibrosis are discussed in the chapter. Cancer is a multigene disease; evidence shows that disruption of the normal functions of several genes is usually required before cancer develops. Cystic fibrosis is the most common inherited disease of European Americans. It is a recessive disorder.