Chromosome

From ArticleWorld

Chromosomes can be thought of as long, continuous pieces of DNA that contain the genetic information in cells. In eukaryotes the uncondensed DNA exists inside the nucleus. Here it wraps around structural proteins, histones, and is called chromatin. During mitosis the chromosomes condense. Each chromosome is composed of two arms the shorter arm called the p arm and the longer one the q arm. Prokaryotes do not have a nucleus or histones and the DNA can be accessed in the relaxed state for replication.

Chromatin

Two types of chromatin have been identified. These are euchromatin and heterochromatin. Euchromatin is made up of active DNA and heterochromatin is made up of inactive DNA. Heterochromatin functions mainly in a structural capacity during the chromosomal stages. When mitosis starts the chromatin strands condense and cease to function as accessible genetic material. They are transformed into a compact transport form and eventually develop into two sister chromatids that become apparent as a chromosome. Once cell division has occurred the chromatids uncoil and again function as chromatin.

Chromosomes and reproduction

It is observed that all normal members of the same species possess the same number of chromosomes. Asexual species have one set of chromosomes that are identical in all cells. Sexually reproducing species have cells that are diploid, that is, they possess two sets of chromosomes, one from the mother and one from the father. The gametes are made by the cell division process of meiosis. The chromosomes of the father and mother can exchange small parts and create new chromosomes not derived solely from any one parent.

Chromosomal aberrations

Chromosomal aberrations can result in genetic disorders. All abnormalities of this type do not result in disease but can lead to an increase in the odds that offspring may be affected. Abnormal numbers of chromosomes may however result indeath or a wide range of genetic disorders. An example of a genetic disorder is Down syndrome. This results from the production of an copy of chromosome 21. This results in a change in physical features as well as some mental retardation. Some others include Cri du chat, Wolf-Hirschhorn syndrome, Edward's syndrome, and XYY syndrome.