Chromosomes are studied by culturing lymphocytes that have been stimulated to divide. Mitosis is then arrested in metaphase by treating the cells with colchicine. At this stage each of the 46 chromosomes is made up of two sister chromatids connected by a centromere responsible for chromosome movements during cell division. When non-metaphase chromosomes are visible as individual rod like structures, the centromere is a central constriction. The tips of chromosomes are called telomeres .
Chromosomes are metacentric if the centromere lies in the middle of the chromosome.
If the centromere is located near one end of the chromosome, it is said to be acrocentric . The very short arms of acrocentric chromosomes are called satellites. When the centromere divides the chromosome into a short arm and a long arm, the short arm is designated p , and the long arm is designated q . Chromosomes derived from lymphocyte culture can be stained with Giemsa stain which produces characteristic light and dark bands on the chromosomes. Most of the 23 pairs of normal chromosomes have a characteristic banding pattern that aids in their identification.