Webster's New World Medical Dictionary

particular gene). The opposite of hetero- is homo-.
heterochromatin
A genetically inactive part of
the genome. Heterochromatin was so named
because its chromosomal material (chromatin)
stains more darkly throughout the cell cycle than
most chromosomal material (euchromatin). There
are two types of heterochromatin: constituitive het-
erochromatin and facultative heterochromatin.
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.
heterochromia iridis, sectoral
A difference in
color within an iris. A person with both brown and
blue in the same eye has sectoral heterochromia
iridis.
heterokaryon
A cell with two separate nuclei
formed by the experimental fusion of two genetically
different cells. For example, heterokaryons com-
posed 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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heteromorphism
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heteroploid
A different chromosome number
than the normal number of chromosomes.
Abnormal numbers of chromosomes are associated
with a number of disorders. For example, Down
syndrome is the result of having three instead of two
chromosome 21s.