Before we begin the tour, the nature of chromosomes and genes must be well understood. Normal human somatic cells have 46 chromosomes: 22 pairs of autosomes (#1-22) and one pair of sex chromosomes (XX or XY). Chromosomes contain genes, which regulate bodily function and development. An individual's chromosomes are inherited from his/her parents. Each parent normally gives a child 23 chromosomes during conception. A child should receive 23 chromosomes from the egg and 23 chromosomes from the sperm. Within the egg and sperm there should be 22 autosomes and one sex chromosome (either an X or Y). Many genetic syndromes, birth defects, and certain types of cancer result from missing, broken, extra or rearranged chromosomes. These chromosomal anomalies can typically be detected through a chromosome analysis.

Cytogenetics is the study of chromosomes. Cytogeneticists recognize and identify chromosome abnormalities by examining chromosomes under a microscope. During a chromosome analysis the 46 chromosomes are aligned into pairs based on physical characteristics (location of centromere, banding pattern) into a karyogram. When paired, differences in the homologues are identified to determine the presence of chromosomal aberrations.