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| Haploid cell |
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A cell containing only one set, or half the usual (diploid) number, of chromosomes.
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| Hemophilia |
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An X-linked recessive genetic disease, caused by a mutation in the gene for clotting factor VIII (hemophilia A) or clotting factor IX (hemophilia B), which leads to abnormal blood clotting.
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| Herbicide |
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Any substance that is toxic to plants; usually used to kill specific unwanted plants.
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| Heterochromatin |
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Dark-stained regions of chromosomes thought to be for the most part genetically inactive.
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| Heteroduplex |
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A double-stranded DNA molecule or DNA-RNA hybrid, where each strand is of a different origin.
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| Heterogeneous nuclear RNA |
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The name originally given to large RNA molecules found in the nucleus, which are now known to be unedited mRNA transcripts, or pre-mRNAs. (See RNA.)
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| HGH |
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See Human growth hormone.
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| hnRNA |
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See Heterogeneous nuclear RNA.
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| Homologous chromosomes |
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Chromosomes that have the same linear arrangement of genes--a pair of matching chromosomes in a diploid organism. See Chromosomes.
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| Homologous recombination |
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The exchange of DNA fragments between two DNA molecules or chromatids of paired chromosomes (during crossing over) at the site of identical nucleotide sequences.
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| Homozygote |
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An organism whose genotype is characterized by two identical alleles of a gene. See Allele, Genotype.
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| Host |
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An organism that contains another organism.
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| Human Genome Project |
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A project coordinated by the National Institutes of Health (NIH) and the Department of Energy (DOE) to determine the entire nucleotide sequence of the human chromosomes. (See NIH.)
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| Human growth hormone (HGH |
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A protein produced in the pituitary gland that stimulates the liver to produce somatomedins, which stimulate growth of bone and muscle.
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| Hybrid |
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The offspring of two parents differing in at least one genetic characteristic (trait). Also, a heteroduplex DNA or DNA-RNA molecule.
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| Hybridization |
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The hydrogen bonding of complementary DNA and/or RNA sequences to form a duplex molecule. (See Northern hybridization, Southern hybridization.)
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| Hybridoma |
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A hybrid cell, composed of a B Iymphocyte fused to a tumor cell, which grows indefinitely in tissue culture and is selected for the secretion of a specific antibody of interest.
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| Hydrogen bond |
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A relatively weak bond formed between a hydrogen atom (which is covalently bound to a nitrogen or oxygen atom) and a nitrogen or oxygen with an unshared electron pair.
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| Hydrolysis |
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A reaction in which a molecule of water is added at the site of cleavage of a molecule to two products.
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