Medical Dictionary Definitions A-Z List
Medical Dictionary Definitions A - Z - «H»:
Herpetiform virus: A virus with the
characteristic shape and behavior of a virus in the herpes
family. Not all members of the herpes virus family have
been identified. Some herpetiform viruses may eventually be
called herpes viruses, while others are merely similar. See herpes virus....
Hershey-Chase experiment: An extraordinarily important experiment in 1952 that helped to convince the world that DNA was the genetic material. Alfred Hershey (1908-1997) and his assistant Martha Chase (1923-2003) at the Cold Spring Harbor Laboratory showed that the DNA, not the protein, of the phage...
Hetero-: Combining form from the Greek "heteros" meaning
"different." The opposite is "homo-" from the Greek "homos" meaning "same." For example, heterogeneous and homogeneous, heterosexual and homosexual, etc....
Heterochromatin: Chromosomal material that is darkly staining and tightly coiled throughout the cell cycle and that is, for the most part, genetically inactive. There are two types of heterochromatin: constitutive heterochromatin and facultative heterochromatin. Constitutive heterochromatin is fixe...
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 c...
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 geneti...
Heterochromia: Different colors....
Heterochromia iridis: A difference of color 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 color within an iris (sectoral 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. (Heterokaryons, for example,
composed of nuclei from Hurler syndrome and Hunter syndrome, both diseases of
mucopolysaccharide metabolism, have normal mucopolysaccharide metabolism prov...
Heteromorphism: Something different in form. Chromosome
heteromorphisms are normal variations in the appearance of chromosomes....
Heterophyes: A minute parasite that lives in the small intestine of humans, cats, dogs and other mammals who acquire it by eating raw or uncooked contaminated fish. Heterophyes is one of the smallest trematodes (parasitic flatworms) infecting humans. The main symptoms are diarrhea and abdominal pain...
Heteroplasia: The replacement of normal tissue of the body by abnormal tissue or by malpositioned normal tissue, a tissue growing in the wrong place.
Progressive osseous heteroplasia is a disorder in which bone develops in areas where bone is normally absent. There is heteroplasia of bone....
Heteroploid: A different chromosome number than the
normal number of chromosomes....