Karyotype

Karyotype is a profile of organism´s chromosomes which are organized by their size, pattern and location of centromere. The order of chromosomes is done according to the size because then it´s easier for specialists to find some disorders. For more information see Chromosome Number and Structure.

Human has 22 pairs of autosomal chromosomes and 1 pair of sex chromosome (X, Y). The common samples are blood cells, bone marrow cells or amniotic fluid (prenatal diagnosis). The whole test of karyotype takes 1-3 weeks (depending on the material used) and it is done in a cytogenetics laboratory.

Normal human DNA is a very long string. When we want to see chromosomes as we are used to see, we have to examine them in their most compact shape. This form is typical for one phase of mitosis - for metaphase. We should stop the growth by using some special chemicals (like colchicine or its synthetic derivates). Also typical stripted pattern is cause by chemicals - e.g. by Giemsa dye - which stain adenine and thymine bases.

How Do We Test Karyotype?

 * 1) Collecting of the samples - the most common are blood cells (especially the white ones - they are actively dividing)
 * 2) Growing of the cells - it is neccesary to cultivate the cells on right medium or cell culture
 * 3) Stoping of the growth - we have to stop dividing in metaphase
 * 4) Dying of chromosomes - chromosomes are normally colorless so we use various staining and banding methods for visualization
 * 5) Sorting of chromosome - from the largest (chromosome 1) to the smallest (chromosome 22)
 * 6) Analysing - structure, pattern, count

Related articles

 * Mitosis
 * Eukaryotic Chromosomes
 * Chromosome
 * Prenatal diagnosis
 * Genetic counseling