1. PATTERNS OF EVOLUTION GLOSSARY
Adaptive feature A structure or way of behaving that help an organism to survive in a
particular environment. Adaptive = survival enhancing.
Adaptive radiation A form of divergent evolution – generally associated with a relatively
rapid divergence into new species or groups and associated with
unoccupied ecological niches.
Allele frequency The proportion of each allele of a particular gene in the gene pool.
Allopoloploidy Where an individual has more than two chromosome sets that have
arisen from combining two different genomes (species) Form
Amphiploidy The doubling of sterile hybrid chromosome sets in plants to create a
Allopatric speciation Pattern of speciation that occurs when organisms or populations are
living in separate geographical areas (ie have become geographically
Analogous organs Organs that are similar in function and often in superficial structure
but of very different evolutionary origins.
Autopolyploidy Where an individual has more than two chromosome sets, that have
arisen from non-disjunction within the same species.
Cline Pattern of variation within a species. A continuous increase or
decrease in some characteristics between adjacent populations as
you move eg North to South.
Co evolution The genetic change (and evolution) in a species, in response to
genetic change in another. Each party in the coevolutionary
partnership exerts selective pressures on the other and over time the
species become mutually dependent.
Convergent evolution The evolution of similar adaptive features in species from different
origins because they have adapted to the same environment.
2. Deme A local unit of population of any one species. They usually have
some genetic or other character that sets them apart from other
Directional selection Natural selection that favours the phenotype of one extreme over the
average or over the other extreme so there is a shift of the average.
Disruptive selection Natural selection that favours both extremes at the expense of the
Divergent evolution Evolution where organisms become more diverse as they evolve
from a common ancestor.
Founder Effect Where only a few organisms move into a new area and may carry
only a few of the available alleles from the species gene pool.
Gene flow The movement of genes from one part of a population to another, or
from one population to another, via gametes.
Gene pool The total of genes in a population at any one time.
Genetic equilibrium. When the allele frequencies of a gene pool remain unchanged from
generation to generation.
Genetic drift Random changes in gene pools(rather than directional ones brought
about by natural selection) Can be highly significant in altering allele
frequency in small gene pools.
Genotype The genetic makeup of an organism – what alleles it carries.
Genotype frequency The proportion of each genotype in the gene pool.
Geographic isolation When physical barriers separate one species population from
Gradualism A theory that states species evolve steadily and gradually change
into different forms.
3. Homologous organs Organs that have descended by inheritance from a common
ancestor, but may have different functions.
Instant speciation When an organism is genetically isolated from its original species in
one generation by polyploidy.
Isolating mechanisms A variety of barriers eg geographical, ecological, temporal, that may
ultimately lead to genetic isolation
Macroevolution Large scale changes in groups of species or genera as viewed in the
fossil record. Evolution above the level of genera.
Microevolution The generation to generation changes in the frequency of alleles or
genotypes in a population.
Mutation A change in a gene that leads to a new allele. Rare and random, but
is the ultimate source of variation for evolution.
Natural selection Process whereby some combinations of alleles are more likely to
help survival and reproduction than others. These are selected in
specific environments, and their frequency will increase in the gene
Niche differentiation How species avoid direct competition with other species by eg
exploiting slightly different food resources.
Pentadactyl limb An example of a homologous organ in vertebrates. “Five-fingered
Phenotype The physical expression of the genotype in an organism.
Phylogeny The evolutionary history of a species or taxonomic group.
Polyploidy Having more than two sets of chromosomes. May bring about the
abrupt formation of a new species.
Population A group of individuals of the same species in an area.
Population Bottlenecks Where a population is reduced to a few survivors whose gene pool is
not necessarily representative of the original gene pool.
4. Postzygotic After fertilization. Refers to isolating factors that prevent successful
reproduction after fertilization.
Prezygotic Before fertilization. Refers to isolation factors that prevent successful
reproduction before fertilization.
Punctuated equilibrium A theory that states that species remain stable for long periods of
time and then undergo relatively rapid speciation and change.
Reproductive isolation. When a species or group can no longer breed successfully with any
other organism but the members of its own species or group.
Ring species Where two apparently different species in one area are joined by a
series of geographical and structural intermediates. Adjacent groups
are still able to interbreed but not the extremes.
Sequential evolution When a species accumulates genetic change over time which result
in a different species (replacing the original rather than branching out
Sexual recombination The shuffling of genes by independent assortment of chromosomes
and random joining of gametes at fertilization.
Species A group of actually or potentially interbreeding natural populations
that is reproductively isolated from other such groups.
Stabilizing selection Natural selection that favours the average phenotype at the expense
of the extremes.
Sympatric speciation Speciation that occurs in species that remain living in the same area
and are never geographically isolated, but become genetically
Vestigal organs Organs that have been important in some ancestral form but that
have become redundant in later species.