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Common Terms

in Evolutionary Biology and Genetics

 

M.Tevfik DORAK

 

On Line Biology Book - Glossary    Glossary of Genetic Terms    Talking Glossary (Genetics)   Gene Reviews: Glossary

Mark Ridley’s Evolution: A - Z

   Life Science Dictionary    Life: The Science of Biology - Glossary    Cytogenetics Glossary

UCMP Glossary (Evolution)    BTO (Genetics)    Population Genetics Glossary

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More Human Genetics Glossaries    Genomic Glossaries & Taxonomies

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Emery’s Elements of Medical Genetics: Glossary

 

Genetic Epidemiology Glossary  

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a-helix: Common secondary 3-dimensional structure of proteins in which the linear sequence of amino acids is folded into a spiral that is stabilized by hydrogen bonds between the carboxyl oxygen of each peptide bond.

Ab initio gene prediction: A computing biology technique that attempts to identify genes without any knowledge of their function nor of the genetics of the organism. This can be accomplished because different gene features, such as exons, introns, promoters, polyadenylation signal etc are associated with unique patterns in the DNA sequence.

Acrocentric chromosome: A chromosome with its centromere towards one end. Human chromosomes 13,14,15,21,22 are acrocentric.

Adaptation: Adjustment to environmental demands through the long-term process of natural selection acting on genotypes.

Adaptive immunity: A collective term for the long-lasting and specific response of lymphocytes to antigens. Requires the MHC, T-cell receptors (TCR) and immunoglobulins (Ig) as well as enzymes with a recombinase activity (for the rearrangements at TCR and Ig gene loci). Present in all vertebrates except jawless fish (see innate immunity).

Additive and non-additive components: In studies of heredity, the portions of the genetic component that are passed and not passed to offspring, respectively.

Advanced (synonym: derived; opposite: primitive): In phylogenetic studies, an organism or character further removed from an evolutionary divergence than a more primitive one.

Agnatha (means jawless): The Class Agnatha represents the most primitive 'jawless' vertebrates. MHC genes have been cloned from all vertebrate classes except Agnatha.

Agrobacterium tumefaciens: A soil bacterium that causes a cancer-like plant disease (crown gall) in dicotyledenous plants (all agricultural crops except cereals). It contains the Ti plasmid. The tumor induction ability of the bacterium spreads to neighbouring cells via the plasmid.

Algae: A heterogeneous group of aquatic, unicellular, colonial or multicellular, eukaryotic and photosynthetic organisms. They belong to the Kingdom Protista and include the multicellular red (rhodophyte), green and brown (kelp) algae. They are not plants but all land plants evolved from the green algae (see also Chromista).

Allee effect: The benefit individuals gain from the presence of conspecifics. Link to a brief explanation of Allee effect.

Allele: A known variation (version) of a particular gene. Formerly called allelomorph.

Allelic association: see linkage disequilibrium.

Allelic exclusion: Expression of only one of the two homologous alleles at a locus in the case of heterozygosity. This usually occurs at loci such as immunoglobulin or T cell receptor (TCR) genes where a functional rearrangement among genes takes place. One of the alleles is either non-functionally or incompletely rearranged and not expressed. This way, each T-cell expresses only one set of TCR genes.

Allelopathy: The influence exerted by a living plant on other plants nearby or microorganisms through production of chemicals. These include 1) carbohydrates and lipids, 2) alkaloids, 3) other nitrogen-containing compounds, 4) flavonoid phenolics and other phenolics, and  5) terpenoids. See reviews (Baldwin, 2003; Bais, 2004).

Allogeneic: Two genetically dissimilar individuals of the same species like any two human beings except monozygotic twins.

Allopatric speciation: Speciation following geographical isolation of subpopulations of the species. See allopatric speciation Java applet at EvoTutor and Speciation in Kimball’s Biology.

Allophenic: Chimeric, i.e., composed of cells of two different genotypes (also called hybrid).

Allometry: A method in morphological evolution that compares differential (nonlinear) growth rates of parts of an organism (isometry describes linear growth rates of parts). See allometry in Mark Ridley’s Evolution: A - Z

Allometry equation: Most lines of relative growth conform to y = bxa where y and x are the two variates being compared, b and a are constants. The value of a, the allometric exponent, is 1 if the growth is isometric (linear); allometry is said to be positive when a>1 and negative when a<1.

Allorecognition: Recognition by T cells of the MHC molecules on an allogeneic individual's antigen-presenting cells, which results in allograft rejection in vivo and mixed lymphocyte reaction (MLR) in vitro.

Altered self: A term used to describe the MHC molecule associated with a peptide rather than in its native form.

Alternation of generations: An alternation of sexual (haploid) and asexual (diploid) form of generations in a life cycle (example: aphids). The relative dominance of each phase is variable in each organism (mosses have a dominant haploid phase whereas angiosperms have a dominant diploid phase).