| heterochromatin | <cell biology, genetics> The chromosomal regions that are condensed during interphase and at the time of nuclear division. They show what is considered an abnormal pattern of staining as opposed to euchromatin. Can be subdivided into constitutive regions (present in all cells) and facultative heterochromatin (present in some cells only). The inactive X chromosome of female mammals is an example of facultative heterochromatin. (18 Nov 1997) |
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| heterochromatin, constituitive | Heterochromatin that is fixed and irreversible. Regions of constituitive heterochromatin are located at very specific spots in the genome (on chromosomes 1, 9, 16 and the y chromosome, the tiny short arms of chromosomes 13-15 and 21 and 22, and near the centromeres of chromosomes) and consists of DNA that contains many tandem (not inverted) repeats of a short basic repeating unit (known as satellite DNA). (12 Dec 1998) |
| heterochromatin, facultative | Heterochromatin that need not always be heterochromatic but has the faculty to return to the normal euchromatic state. The inactive x chromosome is made up of facultatative heterochromatin. When a woman transmits that x to a son, it reverts to euchromatin and genetic activity. (12 Dec 1998) |
| heterochromia | Different colours. (12 Dec 1998) |
| heterochromia iridis | A difference of colour between the iris of one eye and the other. (a person with one brown and one blue eye has heterochromia iridis.) also, a difference in colour within an iris (sectoral heterochromia iridis). (12 Dec 1998) |
| heterochromic cyclitis | A chronic inflammatory cyclitis in which the iris of the affected eye becomes atrophic. (05 Mar 2000) |
| heterochromic uveitis | Anterior uveitis and depigmentation of the iris. Synonym: Fuchs' uveitis. (05 Mar 2000) |
| heterochromosome | <genetics> One or more chromosomes that can be distinguished from autosomes by their morphology and behaviour. Synonym: accessory chromosome, heterochromosome, sex chromosome. (18 Nov 1997) |
| heterochromous | <botany> Having the central florets of a flower head of a different colour from those of the circumference. Origin: Hetero- + Gr. Colour. Source: Websters Dictionary (01 Mar 1998) |
| heterochron | Having varying chronaxies. Origin: hetero-+ G. Chronos, time (05 Mar 2000) |
| heterochronia | Origin or development of tissues or organs at an unusual time or out of the regular sequence. Compare: synchronia. Origin: hetero-+ G. Chronos, time (05 Mar 2000) |
| heterochronic | Relating to heterochronia. Synonym: heterochronic. (05 Mar 2000) |
| heterochronous | Relating to heterochronia. Synonym: heterochronic. (05 Mar 2000) |
| heterochrony | Lack of synchronisation. (18 Nov 1997) |
| heterocladic | Denoting an anastomosis between branches of different arterial trunks, as distinguished from homocladic. Origin: hetero-+ G. Klados, a twig (05 Mar 2000) |