Evolution__3rd_Edition

686 Glossary
isolating mechanism Any mechanism, such as a difference
between species in courtship behavior or breeding season, that
results in reproductive isolation between the species.
isolation Synonym for reproductive isolation.
Lamarckian inheritance A historically misleading synonym
for inheritance of acquired characters.
larva (and larval stage) Prereproductive stage of many
animals; the term is used particularly when the immature stage
has a different form from the adult.
lineage An ancestor–descendant sequence of: (i) populations;
(ii) cells; or (iii) genes.
linkage disequilibrium The condition in which the haplotype
frequencies in a population deviate from the values they would
have if the genes at each locus were combined at random. (When
there is no deviation, the population is said to be in linkage
equilibrium.)
linked Refers to genes present on the same chromosome.
Linnaean classification Hierarchical method of naming classificatory
groups, invented by the eighteenth century Swedish
naturalist Carl von Linné, or Linnaeus. Each individual is assigned
to a species, genus, family, order, class, phylum, and kingdom,
and some intermediate classificatory levels. Species are referred
to by a Linnaean binomial of its genus and species, such as
Magnolia grandiflora. Universally used by educated persons.
locus The location in the DNA occupied by a particular gene.
macroevolution Evolution on the grand scale: the term refers
to events above the species level. The origin of a new higher
group, such as the vertebrates, would be an example of a
macroevolutionary event.
macromutation The mutation of a large phenotypic effect;
one that produces a phenotype well outside the range of variation
previously existing in the population.
mean The average of a set of numbers. For example, the mean
of 6, 4, and 8 is (6 + 4 + 8)/3 = 6.
meiosis A special kind of cell division that occurs during the
reproduction of diploid organisms to produce the gametes.
The double set of genes and chromosomes of the normal diploid
cells is reduced during meiosis to a single haploid set. Crossingover
and therefore recombination occur during a phase of
meiosis.
Mendelian inheritance The mode of inheritance of all diploid
species, and therefore of nearly all multicellular organisms.
Inheritance is controlled by genes, which are passed on to the
offspring in the same form as they were inherited from the previous
generation. At each locus, an individual has two genes, one
inherited from its father and the other from its mother. The two
genes are represented in equal proportions in its gametes.
messenger RNA (mRNA) The kind of RNA produced by transcription
from the DNA and which acts as the message that is
decoded to form proteins.
microevolution Evolutionary changes on the small scale, such
as changes in gene frequencies within a population.
mimicry A case in which one species looks more or less similar
to another species. See Batesian mimicry, Müllerian mimicry.
mitochondrion A kind of organelle in eukaryotic cells; mitochondria
burn the digested products of food to produce energy.
They contain DNA coding for some mitochondrial proteins.
mitosis Cell division. All cell division in multicellular organisms
is by mitosis except for the special division called meiosis
that generates the gametes.
modern synthesis Synthesis of natural selection and Mendelian
inheritance. Also called neo-Darwinism.
molecular clock The theory that molecules evolve at an
approximately constant rate. The difference between the form
of a molecule in two species is then proportional to the time
since the species diverged from a common ancestor, and
molecules become of great value in the inference of phylogeny.
monophyletic group A set of species containing a common
ancestor and all its descendants.
morphology The study of the form, shape, and structure of
organisms.
Müllerian mimicry A kind of mimicry in which two poisonous
species evolve to look like each other.
mutation When parental DNA is copied to form a new DNA
molecule, it is normally copied exactly. A mutation is any
change in the new DNA molecule from the parental DNA
molecule. Mutations may alter single bases, or nucleotides, short
stretches of bases, or parts of or whole chromosomes. Mutations
can be detected both at the DNA level or the phenotypic level.
natural selection The process by which the forms of organisms
in a population that are best adapted to the environment
increase in frequency relative to less well adapted forms over a
number of generations.
neo-Darwinism (i) Darwin’s theory of natural selection plus
Mendelian inheritance. (ii) The larger body of evolutionary
thought that was inspired by the unification of natural selection
and Mendelism. A synonym of modern synthesis.
neutral drift Near synonym of genetic drift.
neutral mutation Mutation with the same fitness as the other
allele (or alleles) at its locus.
neutral theory (and neutralism) A theory that most evolution
at the molecular level occurs by neutral drift.
niche The ecological role of a species: the set of resources it
consumes, and habitats it occupies.
nucleotide A unit building block of DNA and RNA. A
nucleotide consists of a sugar and phosphate backbone with a
base attached.
nucleus The region of eukaryotic cells containing the DNA.
numerical taxonomy In general, any method of taxonomy
using numerical measurements; in particular, it often refers to
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