Chromosomes. Credit: Images

Definition: A chromosome is a long, stringy aggregate of genes that carries heredity information and is formed from condensed chromatin. Chromatin is composed of DNA and proteins that are tightly packed together to form chromatin fibers. Condensed chromatin fibers form chromosomes. Chromosomes are located within the nucleus of our cells. These chromosomes are paired together (one from the mother and one from the father) and are known as homologous chromosomes.

A non-duplicated chromosome is single-stranded and consists of a centromere region that connects two arm regions. The short arm region is called the p arm and the long arm region is called the q arm. The end region of a chromosome is called a telomere. Telomeres consist of repeating non-coding DNA sequences that get shorter as a cell divides.

Chromosome Duplication

Chromosome duplication occurs prior to the division processes of mitosis and meiosis. DNA replication processes allow correct chromosome numbers to be preserved after the original cell divides. A duplicated chromosome is comprised of two identical chromosomes called sister chromatids that are connected at the centromere region. Sister chromatids remain together until the end of the division process where they are separated by spindle fibers and enclosed within separate cells. Once the paired chromatids separate from one another, each is known as a daughter chromosome.

Chromosomes and Protein Production

Protein production is a vital cell process that is dependent upon chromosomes and DNA. DNA contains segments called genes that code for proteins. During protein production, the DNA unwinds and its coding segments are transcribed into an RNA transcript. The RNA transcript is then translated to form a protein.

Chromosome Mutation

Chromosome mutations are changes that occur in chromosomes and are typically the result of either errors that happen during meiosis or by exposure to mutagens such as chemicals or radiation. Chromosome breakage and duplications can cause several types of chromosome structural changes that are typically harmful to the individual. These types of mutations result in chromosomes with extra genes, not enough genes, or genes that are in the wrong sequence. Mutations can also produce cells that have abnormal numbers of chromosomes. Abnormal chromosome numbers typically occur as a result of nondisjunction or the failure of homologous chromosomes to separate properly during meiosis.