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Haploid A cell with half the usual number of
chromosomes, or only one chromosome set. Sex cells
are haploid. Compare Diploid.
Hapten The portion of an antigen that determines
its immunological specificity. When coupled to a
large protein, a hapten stimulates the formation of
antibodies to the two-molecule complex. Also called
antigenic determinant.
Hemagglutination Clumping (agglutination) of red blood
cells.
Heredity Transfer of genetic information from parent
cells to progeny.
Histocompatibility Immunologic similarity of tissues such
that grafting can be done without tissue rejection.
Histocompatibility antigen An antigen that causes the
rejection of grafted material from an animal different
in genotype from the host animal.
Homeobox Family of genes that regulate activities of
other genes (turns genes on and off).
Homologous Corresponding or alike in structure,
position or origin.
Hormone A chemical or protein that acts as a messenger
or stimulatory signal, relaying instructions to stop or
start certain physiological activities. Hormones are
synthesized in one type of cell and then released to
direct the function of other cell types.
Host A cell or organism used for growth of a virus,
plasmid or other form of foreign DNA, or for the
production of cloned substances.
Host-vector system Combination of DNA-receiving cells
(host) and DNA-transporting substance (vector) used
for introducing foreign DNA into a cell.
Human Genome Project An international research effort
aimed at discovering the full sequence of bases in the
human genome. Led in the United States by the National
Institutes of Health and the Department of Energy.
Human immunodeficiency virus (HIV) The virus that
causes acquired immune deficiency syndrome (AIDS).
Hybridization Production of offspring, or hybrids, from
genetically dissimilar parents. The process can be
used to produce hybrid plants (by crossbreeding
two different varieties) or hybridomas (hybrid cells
formed by fusing two unlike cells, used in producing
monoclonal antibodies). See DNA hybridization.
Hybridoma The cell produced by fusing two cells of
different origin. In monoclonal antibody technology,
hybridomas are formed by fusing an immortal cell (one
that divides continuously) and an antibody-producing
cell. See also Monoclonal antibody; Myeloma.
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