Chromosome Structure

The most visible form of chromosomes is the metaphase chromosome. Chromosomes at this stage are used to study chromosome morphology and staining characteristics.

Each metaphase chromosome consists of two sister chromatids, which are attached to the centromere. Telomere refers to the specialized DNA repeat sequences located at the end of chromosomes. The centromere divides a chromosome into a short arm (p; petit) and a long arm (q;queque).

Figure 1:Centromere location

Each chromosome can be classified according to the position of the centromere as:

• Metacentric: The centromere position is in the middle, so the lengths of the two arms are almost equal.
• Submetacentric: One arm (the short) is somewhat shorter than the long arm.
• Acrocentric: The short arm is extremely short. The human genome has six acrocentric chromosomes which include: 13, 14, 15, 21, 22 and Y.
• Telocentric: The centromere position is at the end of chromosome. Humans do not have this type of chromosome.