An image of a person’s complete set of chromosomes is called a karyotype. A karyotype can be used to detect many large chromosome abnormalities. These abnormalities can be either missing, additional, or rearranged chromosomes within a person’s cells. These large scale changes in genetic information can cause a variety of physical and intellectual disabilities.
Cytogenetics is defined as the study of chromosomes. Cytogenetic analysis involves looking at a person’s karyotype and identifying any visible changes. There are several methods of studying a karyotype. One method is to visually match up each pair of chromosomes based on length, centromere location, and banding patterns and determine if any chromosomes are missing, added or rearranged. For the cytogeneticist to visualize the structure and banding pattern of the chromosomes, the patient’s cells should be in the metaphase stage of cell division with the chromosomes condensed. The picture below shows a normal set of chromosomes each lined up with its matching homolog. The person whose karyotype is shown is a male because there is one X and one Y sex chromosome.
|Left: A picture of typical male karyotype.|
Help Me Understand Genetics Handbook. Genetics Home Reference. 2008. U.S. National Library of Medicine. 9 December 2008. http://ghr.nlm.nih.gov/handbook/illustrations/chromosomes
One common way to look at the banding pattern of a chromosome is to stain it with the Giemsa stain. The Giemsa stain is a mixture of methylene blue and eosin. This stain binds to areas of the chromosome with high amounts of Adenine and Thymine bases, making these areas darkly stained. Each chromosome has a distinct banding pattern, so the Giemsa stain can be used to match up homologous chromosomes.
|Left: Interactive karyotyping activity by the Genetic Science Learning Center. Try your hand at matching chromosomes into a karyotype by looking at the Giemsa bands, length, and centromere location.|
“Make a karyotype.” Genetic Science Learning Center. 2008. University of Utah. 10 December 2008. http://learn.genetics.utah.edu/content/begin/traits/karyotype/
|Left: The Karyotyping Activity at The Biology Project, developed at The University of Arizona, will help you use what you have learned about chromosomes and karyotypes to work through real life examples as if you were working in a genetics clinic.|
“Karyotyping Activity.” The Biology Project. 1996. The University of Arizona. 10 December 2008. http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html