Glossary
Genetics glossary
914 definitions · page 9 of 16.
- genetics
- (1) The study of genes through their variation. (2) The study of inheritance.
- genic balance theory
- The theory of Bridges that the sex of a fruit fly is determined by the relative number of X chromosomes and autosomal sets.
- genome
- The entire complement of genetic material in a chromosome set. The entire genetic complement of a prokaryote, virus, mitochondrion or chloroplast or the haploid nuclear genetic complement of a eukaryotic species.
- genomic library
- A set of cloned fragments representing the entire genome of an organism
- genophore
- The chromosome (genetic material) of prokaryotes and viruses.
- genotype
- The specific allelic composition of a cell, either of the entire cell or more commonly for a certain gene or a set of genes. The genes that an organism possesses.
- germ-line theory
- A theory to account for the high degree of antibody variability found in population. The germ-line theory suggests that every B lymphocyte has all the genes for every type of immunoglobulin but transcribes only one. See somatic mutation theory.
- germinal mutation
- mutation occurring in cells that are destined to develop into gametes.
- Giemsa stain
- A complex of stains specific for the phosphate groups of DNA.
- gradient
- A gradual change in some quantitative property over a specific distance.
- gray crescent
- A cortical region of the newly fertilised egg of frogs and some salamanders that forms just after fertilization on the side opposite sperm penetration.
- ground state
- The developmental state of a cell (or group of cells) in the absence of activation of a developmental regulatory switch.
- group 1 intron
- Self-splicing intron that requires an external guanine-containing nucleotide for splicing; releases the intron in a linear form.
- group II intron
- Self-splicing intron that does not require an external nucleotide for splicing; releases the intron in a lariat form.
- group selection
- Selection for traits that would be beneficial to a population at the expense of the individual possessing the trait.
- guanine
- A purine base that pairs with cytosine. See purines.
- guanosine
- The nucleoside having guanine as its base.
- guide RNA (gRNA)
- RNA that guides the insertion of uridines (RNA editing) into mRNAs in trypanosomes. Found in transcripts from minicircles and maxicircles of DNA in kinetoplasts.
- gynandromorph
- An individual that is a mosaic of male and female structures. The underlying cause is frequently sex chromosome mosaicism, such that some cells are chromosomal females while others are chromosomal males. Mosaic individuals having simultaneous aspects of both…
- H-Y antigen
- The histocompatibility Y-antigen, a protein found on the cell surfaces of male mammals.
- haemoglobin (hb)
- The oxygen-transporting blood cell protein in most animals.
- haemophilia
- A disease in which the blood fails to clot. The most common form, primarily affecting males, is caused by a mutation in a gene coding for a clotting protein (factor VIII) inherited as an X-linked recessive phenotype.
- half-chromatid conversion
- A type of gene conversion that is inferred from the existence of non-identical sister spores in a fungal octad showing a non-Mendelian allele ratio.
- haplodiploidy
- The sex-determining mechanism found in some insect groups among which males are haploid and females are diploid
- haploid
- The state of having one copy of each chromosome per nucleus or cell. A cell having one chromosome set, or an organism composed of such cells.
- haploidization
- Production of a haploid from a diploid by progressive chromosome loss.
- haplotype
- A set of closely linked genetic markers present on one chromosome which tend to be inherited together (not easily separable by recombination). Some haplotypes may be in linkage disequilibrium.
- Hardy-Weinberg equilibrium
- The stable frequency distribution of genotypes, AA, Aa, and aa, in the proportions p2, 2pq, and q2 respectively (where p and q are the frequencies of the alleles, A and a) that is a consequence of random mating in the absence of mutation, migration, natural…
- harlequin chromosome
- Sister chromatids that stain differently, so that one appears dark and the other light (harlequin-like).
- HAT medium
- A selection medium for hybrid cell lines; contains hypoxanthine; aminopterin; thymidine. Only cell lines expressing both hypoxanthine phosphoribosyl transferase (HPRT+) and thymidine kinase (TK+) can survive in this medium. Aminopterin inhibits de novo…
- heat-shock protein
- One of a number of proteins appearing in a cell after the cell has been subjected to elevated temperatures.
- helicase
- A protein that unwinds DNA at replication forks.
- helix-turn-helix (HLH) protein
- A protein in which a domain which forms two helices separated by a loop that acts as a sequence-specific DNA binding domain. HLH proteins are thought to act as transcription factors.
- helix-turn-helix motif
- Configuration, found in some DNA-binding proteins, consisting of a recognition helix and a stabilizing helix separated by a short loop.
- hemizygous
- The condition of loci on the X chromosome of the heterogametic sex of a diploid species. Or more generally when one part of the genome, in a normally diploid species, is present in only one copy.
- hemizygous gene
- A gene present in only one copy in a diploid organism for example, X-linked genes in a male mammal.
- heredity
- The biological similarity of offspring and parents.
- heritability
- A measure of the degree to which the variance in the distribution of a phenotype is due to genetic causes. In the broad sense it is measured by the total genetic variance divided by the total phenotypic variance. In the narrow sense it is measured by the…
- heritability in the narrow sense
- The proportion of phenotypic variance that can be attributed to additive genetic variance.
- hermaphrodite
- An individual with both male and female genitalia. (1) A plant species in which male and female organs occur in the same flower of a single individual (compare monoecious plant). (2) An animal with both male and female sex organs.
- heterochromatin
- Densely staining condensed chromosomal regions, believed to be for the most part genetically inert. chromatin that remains tightly coiled (and darkly staining) throughout the cell cycle. See euchromatin
- heteroduplex
- A DNA double helix formed by annealing single strands from different sources; if there is a sequence difference between the strands, the heteroduplex may show single strand loops or bubbles (unpaired regions).
- heteroduplex analysis
- Duplex DNA formed by strands from different sources, referred to as a heteroduplex, will have loops and bubbles in regions where the two DNAs differ. Electron microscopic observation (analysis) of this DNA has been a useful tool in recombinant DNA work.
- heteroduplex DNA model
- A model that explains both crossing over and gene conversion by assuming the production of a short stretch of heteroduplex DNA (formed from both parental DNAs) in the vicinity of a chiasma.
- heteroduplex mapping
- The use of heteroduplex analysis to determine the location of various insertions; deletions; or heterogeneities between two DNA molecules.
- heterogametic sex
- The sex with (usually) two heteromorphic (differently shaped) sex chromosomes (for example, X and Y). During meiosis it produces two kinds of gametes in regard to these sex chromosomes.
- heterogeneous nuclear mRNA (hnRNA)
- The original RNA transcripts found in eukaryotic nuclei before post-transcriptional modifications. A diverse assortment of RNA types found in the nucleus, including mRNA precursors (pre-mRNA) and other types of RNA.
- heterokaryon
- A cell that contains two or more nuclei from different origins. A cell composed of two different nuclear types in a common cytoplasm.
- heterokaryon test
- A test for cytoplasmic organelle mutations (eg. mitochondrial or chloroplast mutations), based on new associations (recombination) of phenotypes in cells derived from genetically marked haploid heterokaryons. Since the heterokaryons are haploid and produce…
- heteromorphic chromosomes
- A chromosome pair with some homology but differing in size, shape, or staining properties. Homologous chromosome pair which are not morphologically identical (eg the sex chromosomes).
- heteroplasmon
- A cell containing a mixture of genetically different cytoplasms, generally different mitochondria or different chloroplasts.
- heteroplasmy
- The existence within an organism of genetic heterogeneity within the populations of mitochondria or chloroplasts.
- heterothallic
- A botanical term used for organisms in which the two sexes reside in different individuals.
- heterothallic fungus
- A fungus species in which two different mating types must unite to complete the sexual cycle.
- heterotroph
- Organism requiring an organic form of carbon as a carbon source.
- heterozygosity
- A measure of the genetic variation in a population; with respect to one locus, stated as the frequency of heterozygotes for that locus.
- heterozygote
- An individual having a heterozygous gene pair. A diploid or polyploid with different alleles at a particular locus.
- heterozygote advantage
- A selection model in which heterozygotes have the highest fitness.
- heterozygous gene pair
- A gene pair having different alleles in the two chromosome sets of the diploid individual for example, Aa or, A1A2.
- hexaploid
- A cell having six chromosome sets, or an organism composed of such cells.