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.

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  • 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.

  • Heteromorphism

    Something that is different in form. Chromosome heteromorphisms are normal variations in the appearance of chromosomes.


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