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Inf & Imm Glossary Homepage
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
Molecular Biology Glossary (ASH) Molecular Biology Glossary (UM) Genome Glossary
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Human Genetics Glossaries Genomic Glossaries & Taxonomies
Conceptual Glossary of Medical Terms
Emery’s Elements of Medical Genetics: 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).