Chromatid

From ArticleWorld

The term chromatid refers to a part of the chromosome when it has coiled together for cell division, be it by mitosis or meiosis. Chromosomes are made up of two chromatids which are identical to each other and joined at a central point to each other. This point of joining is called the centromere. Chromatids are in existence only when the chromosomes start dividing for replication.

Centromere

In chromosomes there is only one centromere. It is only when the process of the cell cycle is initiated that the chromatids are pulled apart. This occurs during anaphase where the mitotic spindle pulls the chromosome causing the split of the two sister chromatids as well as the centromere. When this occurs each chromatid becomes a single chromosome with its own centromere.

Chromosomes

When cells are in their non-dividing stage there are 23 pairs of chromosomes and hence 46 chromatids. It is in the cell division stage that the chromosomes replicate themselves. This results in the production of 92 chromatids just before the cell divides creating two cells each with 46 chromosomes.

In gametic cell division or meiosis the cell replicates itself once however it divides twice thus leaving 23 chromosomes in four cells. These may be four egg or sperm cells. Then on fertilization of the egg by the sperm 23 chromosomes from the female egg is combined with 23 chromosomes from the male and this forms the 46 chromosomes required for zygote formation.