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

Each metaphase chromosome consists of twosister 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

每个染色体可以根据分类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.