Isochromosome


An isochromosome is a structure where a chromosome has lost one of its arms, and the replacement arm is an exact mirror image of the remaining arm.

Isochromosome.gif
Isochromosome.gif


One way that an isochromosome may be formed is by an error in cell division. Before mitosis (or meiosis) a chromosome is replicated to produce two sister chromatids, which together give a sum of two short arms and two long arms. During metaphase of cell division, a chromosome may accidentally line up on the metaphase plate perpendicularly to the plane of all the other chromosomes. This causes the chromosome to be divided at its centromere in such a way that the long arms remain together, as do the short arms; the resulting structures are isochromosomes.