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| Gene flow |
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The exchange of genes between different but (usually) related populations.
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| Gene frequency |
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The percentage of a given allele in a population of organisms. See Allele.
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| Gene insertion |
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The addition of one or more copies of a normal gene into a defective chromosome.
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| Gene linkage |
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The hereditary association of genes located on the same chromosome.
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| Gene modification |
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The chemical repair of a gene's defective DNA sequence. See DNA.
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| Gene pool |
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The totality of all alleles of all genes of all individuals in a particular population.
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| Gene splicing |
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Combining genes from different organisms into one organism. See recombinant DNA.
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| Gene translocation |
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The movement of a gene fragment from one chromosomal location to another, which often alters or abolishes expression.
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| Genetic assimilation |
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Eventual extinction of a natural species as massive pollen flow occurs from another related species and the older crop becomes more like the new crop. See Gene flow.
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| Genetic code |
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The three-letter code that translates nucleic acid sequence into protein sequence. The relationships between the nucleotide base-pair triplets of a messenger RNA molecule and the 20 amino acids that are the building blocks of proteins. See Base pair, Nucleic acid, Nucleotide.
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| Genetic disease |
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A disease that has its origin in changes to the genetic material, DNA. Usually refers to diseases that are inherited in a Mendelian fashion, although noninherited forms of cancer also result from DNA mutation.
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| Genetic drift |
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Random variation in gene frequency from one generation to another.
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| Genetic engineering |
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The manipulation of an organism's genetic endowment by introducing or eliminating specific genes through modern molecular biology techniques. A broad definition of genetic engineering also includes selective breeding and other means of artificial selection.
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| Genetic linkage map |
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A linear map of the relative positions of genes along a chromosome. Distances are established by linkage analysis, which determines the frequency at which two gene loci become separated during chromosomal recombination. (See Mapping.)
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| Genetic marker |
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A gene or group of genes used to "mark" or track the action of microbes.
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| Genome |
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The genetic complement contained in the chromosomes of a given organism, usually the haploid chromosome state.
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| Genomic library |
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A library composed of fragments of genomic DNA. (See Library.)
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| Genotype |
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The structure of DNA that determines the expression of a trait. See Phenotype.
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| Genus |
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A category including closely related species. Interbreeding between organisms within the same category can occur.
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| GEO |
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Genetically engineered organism.
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| Germ cell |
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Reproductive cell. See Somatic cell.
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| Germ cell (germ line) gen |
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The repair or re- placement of a defective gene within the gamete-forming tissues, which produces a heritable change in an organism's genetic constitution.
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| GMO |
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Genetically modified organism.
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| Green revolution |
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Advances in genetics, petrochemicals, and machinery that culminated in a dramatic increase in crop productivity during the third quarter of the 20th century.
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| Growth curve |
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See Growth phase.
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| Growth factor |
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A serum protein that stimulates cell division when it binds to its cell-surface receptor.
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| Growth phase (curve). |
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The characteristic periods in the growth of a bacterial culture, as indicated by the shape of a graph of viable cell number versus time. (See Death phase, Lag phase, Logarithmic phase, Stationary phase.)
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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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| Immortalizing oncogene |
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A gene that upon transfection enables a primary cell to grow indefinitely in culture. (See Oncogene.)
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| In situ |
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Refers to performing assays or manipulations with intact tissues.
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| In vivo |
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Refers to biological processes that take place within a living organism or cell.
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| Incomplete dominance |
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A condition where a heterozygous off- spring has a phenotype that is distinctly different from, and intermediate to, the parental phenotypes. See Heterozygote, Phenotype.
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