MODEL RELEASED. Chromosome analysis. Geneticist analysing human chromosomes by fluorescent microscopy. Individual chromosomes are visible on the computer monitor as pale blue rods. They have been stained using dyes that fluoresce under light from the microscope (centre). The circular objects are cell nuclei. Chromosomal analysis is used as a diagnostic technique to detect abnormalities responsible for genetic diseases such as Down's syndrome. Most human cells contain 23 pairs of chromosomes. They are made up of the genetic material DNA (deoxyribonucleic acid), and together contain the instructions necessary for the development and functioning of human life.