Scientists use three main techniques to study chromosomes: 

Karyotyping

A karyotype refers to a single person’s set of chromosomes. Karyotyping is a way of looking at a set of chromosomes that the individual has. In this technique, chromosomes are treated with stains that generate distinctive light and dark stripes called bands so they can be seen under a microscope. The chromosome pairs are arranged into a standardized format or karyotype. Karyotypes are distinctly uniform among the members of a species, making it possible for cytogeneticists to detect aberrations in the number or structure of chromosomes.

Fluorescence in situ hybridization (FISH)

In the FISH technique, cells in a sample are treated with fluorescent dyes that only bind to specific parts of chromosomes. When the stained cells are viewed under a microscope using a special list, researchers can identify chromosome deviations that are not visible using standard cytogenetic testing. 

Chromosomal microarray analysis (CMA)

In chromosomal microarray analysis, the DNA sample is stained with a fluorescent dye and then analyzed using specialized equipment that highlights if there are extra chromosome pieces or if any chromosome pieces are missing. CMA allows researchers to detect chromosome abnormalities with more detail than either karyotyping or FISH.