Chromosomal aberrations are abnormalities in the structure or number of chromosomes and are often responsible for genetic disorders. For more than a century, scientists have been fascinated by the study of human chromosomes. It was not until 1956, however, that it was determined that the actual diploid number of chromosomes in a human cell was forty-six (22 pairs of autosomes and two sex chromosomes make up the human genome). In 1959 two discoveries opened a new era of genetics. Jerome Lejeune, Marthe Gautier, and M. Raymond Turpin discovered the presence of an extra chromosome in Down syndrome patients. And C. E. Ford and his colleagues, P. A. Jacobs and J. A. Strong first observed sex chromosome anomalies in patients with sexual development disorders.

Advances in Chromosomal Analysis

Identification of individual chromosomes remained difficult until advances in staining techniques such as Q-banding revealed the structural organization of chromosomes. The patterns...