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chromosome
(kro´mә-sōm)
in eukaryotes, a structure in the cell nucleus that contains a linear thread of deoxyribonucleic acid (DNA) the transmitter of genetic information. During cell division the chromosomal material is compactly coiled, making it
visible with appropriate staining and permitting its movement in the cell with minimal entanglement. Each member of a species
is normally characterized by the same number of chromosomes in its somatic cells. In humans, the usual number is 46, including
22 pairs of autosomes and the two sex chromosomes (XX or XY) that determine the sex of the organism. (See also heredity and karyotype.) adj., chromoso´mal., adj.
Chromosome. (A), Long, threadlike interphase chromatin in nucleus. (B), Giemsa-stained, partially condensed chromatid in late prophase. (C), Giemsa-stained, fully condensed chromatid in metaphase; note that some of the sub-bands visible in late prophase have condensed
into single bands. (In B and C, only one of a pair of sister chromatids is shown.)
the term has been extended to refer to the analogous structure carrying genetic material in prokaryotes, mitochondria, and chloroplasts, which is a closed circle of double-stranded DNA.
Copyright 2007. An Elsevier publication. All rights reserved.
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