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Modern Genetic Analysis Glossary
G
G Guanine or guanosine.
G0 phase The resting phase that can occur in G1 of interphase of the cell cycle.
G1 phase The part of interphase of the cell cycle that precedes S phase.
G2 phase The part of interphase of the cell cycle that follows S phase.
gain-of-function dominant mutation One subset of all dominant mutations, in which the mutational event causes the protein to have a new function, through altered protein structure or through elevated or ectopic expression of the normal gene product.
gain-of-function mutation A mutation that results in a new functional ability for a protein, detectable at the phenotypic level.
gamete A specialized haploid cell that fuses with a gamete from the opposite sex or mating type to form a diploid zygote; in mammals, an egg or a sperm.
gametophyte The haploid gamete-producing stage in the life cycle of plants; prominent and independent in some species but reduced or parasitic in others.
gap gene In Drosophila, a class of cardinal genes that are activated in the zygote in response to the anteriorposterior gradients of positional information. Through regulation of the pair-rule and homeotic genes, the patterns of expression of the various gap gene products lead to the specification of the correct number and types of body segments. Gap mutations cause the loss of several adjacent body segments.
gastrulation The first process of movements and infoldings of the cell sheet in early animal embryos, usually immediately after formation of the blastula (or blastoderm).
gene The fundamental physical and functional unit of heredity, which carries information from one generation to the next; a segment of DNA, composed of a transcribed region and a regulatory sequence that make transcription possible.
gene amplification The process by which the number of copies of a chromosomal segment is increased in a somatic cell.
gene conversion A meiotic process of directed change in which one allele directs the conversion of a partner allele into its own form.
gene disruption Inactivation of a gene by the integration of a specially engineered introduced DNA fragment.
gene dose The number of copies of a particular gene pres-ent in the genome.
gene family A set of genes in one genome all descended from the same ancestral gene.
gene frequency See allele frequency.
gene fusion The accidental joining of DNA of two genes, such as can occur in a translocation. Gene fusions can give rise to hybrid proteins or to the misregulation of the transcription unit of one gene by the cis-regulatory elements (enhancers) of another.
gene interaction The collaboration of several different genes in the production of one phenotypic character (or related group of characters).
gene locus The specific plate on a chromosome where a gene is located.
gene map A linear designation of mutant sites within a gene, based on the various frequencies of interallelic (intragenic) recombination.
gene mutation A point mutation that results from changes within the structure of a gene.
gene pair The two copies of a particular type of gene pres-ent in a diploid cell (one in each chromosome set).
gene rearrangement The process of programmed changes in the DNA structure of somatic cells, leading to changes in gene number or in the structural and functional properties of the rearranged gene.
gene replacement The insertion of a genetically engineered transgene in place of a resident gene; often achieved by a double crossover.
gene therapy The correction of a genetic deficiency in a cell by the addition of new DNA and its insertion into the genome.
generalized transduction The ability of certain phages to transduce any gene in the bacterial chromosome.
genetic code The set of correspondences between nucleotide pair triplets in DNA and amino acids in protein.
genetic dissection The use of recombination and mutation to piece together the various components of a given biological function.
genetic markers Alleles used as experimental probes to keep track of an individual, a tissue, a cell, a nucleus, a chromosome, or a gene.
genetic variance The phenotypic variance associated with the average difference in phenotype among different genotypes.
genetics (1) The study of genes. (2) The study of inheritance.
genome The entire complement of genetic material in a chromosome set.
genomic library A library encompassing an entire genome.
genomics The cloning and molecular characterization of entire genomes.
genotype The specific allelic composition of a celleither of the entire cell or, more commonly, of a certain gene or a set of genes.
germ line The cell lineage in a multitissued eukaryote from which the gametes derive.
germinal mutations Mutations occurring in the cells that are destined to develop into gametes.
Gln Glutamine (an amino acid).
Glu Glutamate (an amino acid).
Gly Glycine (an amino acid).
G-protein A member of a family of proteins that contribute to signal transduction through proteinprotein interactions that take place when the G-protein binds GTP but not when the G-protein binds GDP.
gradient A gradual change in some quantitative property over a specific distance.
ground state The developmental state of a cell (or group of cells) in the absence of activation of a developmental regulatory switch.
growth factors Paracrine signaling molecules, usually secreted polypeptides, that induce cell division in cells receiving these signals.
guanine A purine base that pairs with cytosine.
guanosine The nucleoside having guanine as its base.
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, whereas others are chromosomal males.

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