Glossary

Genetics glossary

914 definitions · page 10 of 16.

Hfr: High frequency of recombination. A strain of bacteria that has incorporated an F factor into its chromosome and can then transfer the chromosome during conjugation. In Escherichia coli, a cell having its fertility factor integrated into the bacterial…
Himalayan: A mammalian temperature-dependent coat phenotype, generally albino with pigment only at the cooler tips of the ears, feet, and tail.
His: Histidine (an amino acid).
histocompatibility antigen: antigen that determines acceptance or rejection of a tissue graft by the immune system.
histocompatibility gene: A gene encoding an histocompatibility antigen.
histone: A type of basic protein that forms the unit around which DNA is coiled in the nucleosomes of eukaryotic chromosomes. Arginine and lysine rich basic proteins making up a substantial portion of eukaryotic nucleoprotein.
holandric trait: Trait controlled by a locus found only on the Y chromosome. Involves father to son transmission.
holoenzyme: The complete enzyme including all subunits. Often used in reference to RNA and DNA polymerases.
homeo-box: A consensus sequence of about 180 base pairs discovered in homeotic genes in Drosophila. Also found in other developmentally important genes from yeast to human beings. A family of quite similar l80base-pair DNA sequences that encode a polypeptide sequence…
homeo-domain: An approximately sixty-amino acid protein domain translated from the homeo-box. A highly conserved family of protein domain sequences 60 amino acids in length found within a large number of transcription factors that can form a helix-turn-helix structure and…
homeologous chromosomes: Partially homologous chromosomes, usually indicating some original ancestral homology.
homeosis: The replacement of one body part by another. Homeosis can be caused by environmental factors leading to developmental anomalies, or by mutation.
homeotic mutations (genes): Mutations (defining genes) with a phenotype in which a given cell develops along a pathway normally followed by a different cell type. Mutations that can change the fate of an imaginal disk in insect development.
homogametic sex: The sex with homomorphic (similarly shaped) sex chromosomes (for example, XX), producing only one kind of gamete in regard to the sex chromosomes.
homologous chromosomes: Members of a pair of essentially identical chromosomes that synapse during meiosis. Chromosomes that pair with each other at meiosis or chromosomes in different species that have retained most of the same genes during their evolution from a common ancestor.
homologous recombination: Breakage and reunion between homologous lengths of DNA mediated in Escherichia coli by products of the genes RecA and RecBCD, and functionally equivalent genes in other organisms.
homologue: A member of a pair of homologous chromosomes.
homomorphic chromosomes: Morphologically identical members of a homologous pair of chromosomes.
homoplasmy: The existence within an organism of only one type of plastid; usually referring to genetic identity of mitochondria or chloroplasts.
homothallic: A botanical term used for groups whose individuals are not of different sexes.
homothallic fungu: A fungus species in which a single sexual spore can complete the entire sexual cycle (compare heterothallic fungus).
homozygote: An individual having a homozygous gene pair. A diploid or a polyploid with identical alleles at a locus.
homozygous gene pair: A diploid gene pair having identical alleles in both copies for example, AA or, aa.
hormone: Chemical secreted by one type of cell and acting on a second type of cell.
hormone response element (HRE): An HRE is a cis-regulatory DNA sequence for a hormone that acts by binding to a receptor that can act as a transcription factor, that is a binding site for the hormone-receptor complex.
host range: 1. The spectrum of strains of bacterial species that a given strain of phage can infect. 2. The range of cells that can act as a host to a virus or bacteriophage.
hot spot: A region of a genome exhibiting an increased frequency of some genetic phenomenon such as mutation, recombination and transposition.
Huntington's disease: A late but variable age onset lethal human disease of nerve degeneration. Inherited as an autosomal dominant phenotype. Shows imprinting individuals inheriting HD from their father show significantly earlier onset than those inheriting a maternal allele…
hybrid: (1) A heterozygote. (2) A progeny individual from any cross involving parents of differing genotypes. Offspring of unlike parents. (3) A duplex polynucleotide formed by hybridization of two single stranded polynucleotides of different origin.
hybrid DNA: DNA whose two strands have different origins.
hybrid dysgenesi: A syndrome of effects including sterility, mutation, chromosome breakage, and male recombination in the hybrid progeny of crosses between certain laboratory and natural isolates of Drosophila.
hybrid plasmid: A plasmid that contains an inserted piece of foreign DNA.
hybrid vector hybrid vehicle: An episome or plasmid containing an inserted piece of foreign DNA.
hybrid vector/hybrid vehicle: An episome or plasmid containing an inserted piece of foreign DNA.
hybrid zone: Geographical region in which previously isolated populations that have evolved differences come into contact and form hybrids.
hybridization in situ: Finding the location of a gene or gene product by adding specific radioactive or chemically tagged probes for the gene and detecting the location of the radioactivity or chemical on the chromosome or in the cell after hybridization.
hybridize: (1) To form a hybrid by performing a cross. (2) To anneal nucleic acid strands from different sources.
hybridoma: A cell resulting from the fusion of a spleen cell and myeloma cell. These cells can be cloned and maintained indefinitely in cell culture and produce monoclonal antibodies.
hydrogen bond: A weak bond involving the sharing of an electron with a hydrogen atom; hydrogen bonds are important in the specificity of base pairing in nucleic acids and in the determination of protein shape.
hydroxyapatite: A form of calcium phosphate that binds double-stranded DNA.
hypermorph: A mutant with more than the normal amount of some gene product.
hyperploid: Aneuploid containing a small number of extra chromosomes.
hypervariable locus: locus with many alleles; especially those whose variation is due to variable numbers of tandem repeats.
hypervariable region: The part of a variable region that actually determines the specificity of an immunoglobulin.
hypha (plural hyphae): A thread-like structure (composed of cells attached end to end) that forms the main tissue in many fungus species.
hypomorph: A mutant with less than the normal amount of some gene product.
hypoploid: Aneuploid with a small number of chromosomes missing.
hypostatic gene: A gene whose expression is masked by an epistatic gene.
identity by descent: The state of two alleles when they are identical copies of the same ancestral allele (autozygous).
idiogram: A photograph or diagram of the chromosomes of a cell arranged in an orderly fashion. See karyotype.
idiotypic variation: Variation unique to an individual immunoglobulin molecule produced by the variable region of immunoglobulin genes.
idling reaction: The production of guanosine tetraphosphate (3' ppGpp 5', magic spot) by the stringent factor when a ribosome encounters an uncharged tRNA in the A site.
imago: An adult insect.
immune system: The cells and tissues involved in recognizing and attacking foreign substances within the body of an animal.
immunity: The ability of an organism to resist infection.
immunoglobulin (Ig): A general term for the kind of globular blood proteins that constitute antibodies. A tetrameric protein composed of two identical light chains and two identical heavy chains. Specific proteins produced by derivatives of B lymphocytes that interact with and…
immunoglobulin gene: A gene encoding one of the protein chains (light or heavy) of an immunoglobulin. The germline genes are activated by a special recombination process that joins a number of different gene segments together. In the case of immunoglobulin light chains there are…
immunohistochemistry: The use of antibodies or antisera as histological tools for identifying patterns of antigen distribution within a tissue or an organism. An antibody (or mixture of antibodies) that binds to a specific protein or other antigen is tagged with a fluorescent…
in vitro: In an experimental situation outside the organism. Biological or chemical work done in the test tube (literally in glass) rather than in living systems.
in vitro mutagenesis: The production of either random or specific mutations in a piece of cloned DNA. Typically, the DNA will then be reintroduced into a cell or an organism to assess the results of the mutagenesis.