A karyotype is a picture in which the chromosomes of a cell
have been stained so that the banding patterns of the chromosomes appear. This
way it is possible to view abnormalities in the chromosomes. Disorders such as aneuploidy can be diagnosed by karyotype.
It can also help identify local abnormalities on chromosomes such as abnormalities
in chromosome length, and location of the
centromere.
Every cell of the organism has the same DNA sequence and same genes. However, not all genes are expressed in every single cell at the same time. Only those genes necessary for a specialised function of a specialised cell are expressed in the specialised cell. For example, skin cells have some different proteins than nerve cells. Genes responsible for those "skin proteins" are activated in skin cells and are turned off in nerve cells.
