Types Of Chromosomes

A chromosome is marked by a constriction known as primary constriction. The primary constriction divides the chromosome into two arms. In the region of primary constriction lies the centromere. It is associated with granule like structure made of protein the kinetochore, to which spindle fibers attach during cell division. 

Structure of an Anaphase Chromosome

A chromosome may have one more constriction. It is called secondary constriction. The tip of the chromosomes are rounded and sealed and are called telomeres. The terminal part of the chromosome beyond secondary constriction is called satellite. Based on the location of primary constriction and kinetochore, the chromosomes are described as:

Types of Chromosomes 

Metacentric

These are V-shaped chromosomes, have centromere in the middle so that the two arms of the chromosomes are almost equal.

Sub-metacentric

These are L-shaped chromosomes with centromere slightly away from the midpoint so that the two arms of the chromosome are almost equal.

Acrocentric

These are rod shaped chromosomes with terminal centromere, so that they possess only one arm.

Telocentric

These are also rod-shaped but with sub-terminal centromere have one arm very long and the other arm is very short.

Karyotype

When chromosomes are arranged by pairs according to their size, shape and general appearance in mitotic metaphase it is called karyotype. It is the total chromosomal complement of a cell. Study of karyotype is used for the identification of chromosomal number. The figure below outlines the steps in one method of preparation of a karyotype from a blood sample. Karyotyping is used to screen the abnormal number of chromosomes and for defective ones. 

Preparation of Human Karyotype