Heterochromatin, constitutive
Heterochromatin that is fixed and irreversible. Regions of constitutive 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).
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- Heterochromatin, facultative
Heterochromatin that need not always be heterochromatic but which has the faculty to return to the normal euchromatic state. The inactive X chromosome is made up of facultative heterochromatin. When a woman transmits that X to a son, it reverts to euchromatin and genetic activity.
- Heterochromia iridis
A difference in color between the iris of one eye and the iris of the other eye. A person with one brown eye and one blue eye has heterochromia iridis.
- Heteroclite
Deviating from the ordinary; irregular or abnormal; anomalous. As, for example, retroviruses represent a heteroclite field of virology. From the Greek hetero- (different) + klinein (to lean, inflect).
- Heteroerotic
Having to do with sexual excitement toward the opposite sex. By contrast with alloerotic.
- Heterokaryon
A cell with two separate nuclei formed by the experimental fusion of two genetically different cells. For example, heterokaryons composed of nuclei from Hurler syndrome and Hunter syndrome, both diseases of mucopolysaccharide metabolism, have normal mucopolysaccharide metabolism. This proves that the two syndromes affect different proteins and so can correct each other in the heterokaryon.