| HP1 | Heterochromatin Protein 1 |
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| facultative heterochromatin | <cell biology> The heterochromatin which is condensed in some cells and not in others, presumably representing stable differences in the activity of genes in different cells. The best known example results from the random inactivation of one of the pair of X chromosomes in the cells of female mammals, (Lyonisation). (18 Nov 1997) |
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| 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) |
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| constitutive heterochromatin | <protein> Regions on chromosomes which are permanently condensed and genetically inactive in every cell in the body. The condensed portions are always in the same position on both homologous chromosomes. An example is the centromeres. Compare: facultative heterochromatin. (09 Oct 1997) |
| satellite-rich heterochromatin | Heterochromatin that codes for 18 S and 28 S components of ribosomal RNA and is located close to the centromeres of certain chromosomes. (05 Mar 2000) |
| 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) |
| 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) |
| facultative | Of parasites, optional. Compare: obligate. (09 Oct 1997) |
| facultative aerobe | <microbiology> An organism which is normally anaerobic but can also grow in the presence or oxygen. (15 Nov 1997) |
| facultative anaerobe | <microbiology> A microorganism which can survive without oxygen (is an anaerobe) but is not harmed if oxygen is present. (09 Oct 1997) |
| facultative hyperopia | Hyperopia that can be compensated by accommodation. Synonym: facultative hyperopia. (05 Mar 2000) |
| facultative parasite | An organism that may either lead an independent existence or live as a parasite, in contrast to obligate parasite. (05 Mar 2000) |
| facultative ponds | Ponds having an aerobic zone on the top and an anaerobic zone on the bottom. (05 Dec 1998) |
| facultative species | <ecology> Species that can occur both in wetlands and uplands, there are three subcategories of facultative species: 1. Facultative wetland plants (FACW) that usually occur in wetlands (estimated probability 67-99%), but occasionally are found in nonwetlands. 2. Facultative plants (FAC) that are equally likely to occur in wetlands or nonwetlands (estimated probability 34-66%). 3. Facultative upland plants (FACU) that usually occur in nonwetlands (estimated probability 67-99%), but occasionally are found in wetlands (estimated probability (1-33%). (09 Oct 1997) |
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