Composed of chromatin, these thread-like bodies of linearly arranged genes carry the information that results in inherited traits. DNA and/or RNA are attached to protein.

In any one kind of plant or animal, the chromosome count is usually constant in their cells. Humans have 46 chromosomes. Females have two X chromosomes, males have X and Y chromosomes. (YY doesn't work, the fetus doesn't develop.)

A chromosome consists of a single double helix of DNA wrapped around a protein scaffold. Two main types of chromosome exist - linear and circular. Circular chromosomes are pretty much limited to the prokaryotes, while linear ones are found in both prokaryotes and eukaryotes. Chromosomes may be divided into euchromatin and heterochromatin sections. Euchromatin is DNA that is less tightly folded around the scaffold, allowing it to be accessed by RNA polymerase and various other DNA binding proteins. Heterochromatin is the DNA that is tightly folded and contains genes that are not currently being transcribed along with sections of DNA that contain no genes. Linear chromosomes also have telomeres, sections of DNA at each end that can be replicated without using DNA polymerase and thus preventing the chromosome becoming shorter each time it's replicated, and centromeres, the point at which the two chromatids present during DNA replication are joined together.

Chro"mo*some` (?), n. [Gr. color + the body.] Biol.

One of the minute bodies into which the chromatin of the nucleus is resolved during mitotic cell division; the idant of Weismann.


© Webster 1913.

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