Evolution__3rd_Edition

684 Glossary
individuals, such as populations or species (phenetic distance),
or the difference in their gene frequencies (genetic distance).
DNA Deoxyribose nucleic acid, the molecule that controls
inheritance.
dominance (genetic) An allele (A) is dominant if the phenotype
of the heterozygote Aa is the same as the homozygote AA. The
allele a does not influence the heterozygote’s phenotype and is
called recessive. An allele may be partly, rather than fully, dominant:
then the heterozygous phenotype is nearer to, rather than
identical with, the homozygote of the dominant allele.
drift Synonym of genetic drift.
duplication The occurrence of a second copy of a particular
sequence of DNA. The duplicate sequence may appear next to
the original, or be copied elsewhere into the genome. When the
duplicated sequence is a gene, the event is called gene duplication.
A distinction exists between the mutation that creates a
duplication, and the evolutionary process that substitutes a
duplicated form of a gene. The word is sometimes used to refer
to the mutation, and sometimes to the combination of the
mutation and its substitution.
ecological genetics Study of evolution in action in nature, by
a combination of fieldwork and laboratory genetics.
ecological species concept A concept of species, according
to which a species is a set of organisms adapted to a particular,
discrete set of resources (or “niche”) in the environment.
Compare biological species concept, phenetic species concept,
recognition species concept.
electrophoresis A method of distinguishing entities according
to their motility in an electric field. In evolutionary biology,
it has been mainly used to distinguish different forms of proteins.
The electrophoretic motility of a molecule is influenced by
its size and electric charge.
epistasis An interaction between the genes at two or more loci,
such that the phenotype differs from what would be expected if
the loci were expressed independently.
eukaryote Made up of eukaryotic cells. Almost all multicellular
organisms are eukaryotic. Compare prokaryote.
eukaryotic cell A cell with a distinct nucleus.
eutherian (Eutheria) One of two or three major subdivisions
of mammals. The other two are Prototheria (echidnas) and
Metatheria (marsupials). Most familiar mammals (at least,
outside Australia) are eutherians: cats, elephants, dolphins,
monkeys, and rodents are all eutherians.
evo-devo The term used for research on the relation between
individual development (from egg to adult) and evolution.
evolution Darwin defined it as “descent with modification.” It
is the change in a lineage of populations between generations.
evolutionary classification The method of classification
using both cladistic and phenetic classificatory principles. To be
exact, it permits paraphyletic groups (which are allowed in phe-
netic but not in cladistic classification) and monophyletic groups
(which are allowed in both cladistic and phenetic classification)
but excludes polyphyletic groups (which are banned from cladistic
classification but permitted in phenetic classification).
exon The nucleotide sequences of some genes consist of parts
that code for amino acids, and other parts interspersed among
them that do not code for amino acids. The coding parts, which
are translated, are called exons; the interspersed non-coding
parts are called introns.
fitness The average number of offspring produced by individuals
with a certain genotype, relative to the number produced
by individuals with other genotypes. When genotypes differ
in fitness because of their effects on survival, fitness can be
measured as the ratio of a genotype’s frequency among the
adults divided by its frequency among individuals at birth.
fixation A gene has achieved fixation when its frequency has
reached 100% in the population.
fixed (i) In population genetics, a gene is “fixed” when it has a
frequency of 100%. (ii) In the theory of separate creation, species
are described as “fixed” in the sense that they are believed not to
change their form, or appearance, through time.
founder effect The loss of genetic variation when a new
colony is formed by a very small number of individuals from a
larger population.
frequency-dependent selection Selection in which the
fitness of a genotype (or phenotype) depends on its frequency in
the population.
gamete The haploid reproductive cells that combine at fertilization
to form the zygote: sperm (or pollen) in the male and
eggs in females.
gene Sequence of nucleotides coding for a protein (or, in some
cases, part of a protein).
gene duplication See duplication.
gene family A set of related genes occupying various loci in the
DNA, almost certainly formed by duplication of an ancestral
gene, and having recognizably similar sequence. The globin
gene family is an example.
gene flow The movement of genes into, or through, a population
by interbreeding or by migration and interbreeding.
gene frequency The frequency in the population of a particular
gene relative to other genes at its locus. Expressed as a
proportion (between 0 and 1) or percentage (between 0%
and 100%).
gene pool All the genes in a population at a particular time.
genetic code The code relating nucleotide triplets in the
messenger RNA (or DNA) to amino acids in the proteins. It has
been decoded (see Table 2.1, p. 26).
genetic distance See distance.
genetic drift Random changes in gene frequencies in a
population.
..