Chro"ma*tin(?), n. (Biol.) The deeply staining substance of the nucleus and chromosomes of eukaryotic cells, composed of DNA and basic proteins (such as histones), the DNA of which comprises the predominant physical basis of inheritance. It was, at the beginning of the 20th century, supposed to be the same substance as was then termed idioplasm or germ plasm. In most eukaryotic cells, there is also DNA in certain plasmids, such as mitochondria, or (in plant cells) chloroplasts; but with the exception of these cytoplasmic genetic factors, the nuclear DNA of the chromatin is believed to contain all the genetic information required to code for the development of an adult organism. In the interphase nucleus the chromosomes are dispersed, but during cell division or meiosis they are condensed into the individually recognizable chromosomes. The set of chromosomes, or a photographic representation of the full set of chromosomes of a cell (often ordered for presentation) is called a karyotype.
[Webster 1913 Suppl.]
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