Definitions for evolution (Biology 3

							                                               Definitions for Evolution
                                                     (Biology 3.5)
To revise, cover the right-hand side of the table with a sheet of paper and move down the left column seeing which words
you already know the definitions of (slide the paper down a word at a time to check). Tick these ones off, and concentrate
on the others until you have learnt them all. Then cover the left-hand side of the table and have a go at writing the words
to match the definitions!
The shaded words are less important.

Adaptive radiation             Pattern of evolution where a large number of species form to occupy
                               different ecological niches.
Allopatric                     Type of speciation as a result of geographical isolation.
Analogous structures           Features that have similar form/function – a result of convergence.
Co-evolution                   Pattern of evolution where one species or group changes its genetic
                               composition in response to a genetic change in another.
Convergent evolution           Pattern of evolution where different species living in a similar environment
                               come to look similar.
Deme                           A group of individuals of a species that have many features in common.
                               Another word used is ‘race’.
Directional selection          When one extreme is selected for.
Disruptive selection           Where both extremes are selected for against the middle range. This
                               ultimately produces two new species.
Divergent evolution            When one species branches to form two or three species.
Gene pool                      All the genes in a reproducing population.
Genetic drift                  Random changes in allele frequencies because of small population size.
Genome                         The genetic make-up of an individual.
Gradualism                     Pattern of evolution where slow changes between populations occur as a
                               result of different selection pressures.
Hybrid                         The product of a cross between 2 different species.
Homologous structure           Structures with common ancestry, now used for differing functions.
Instant Speciation             Speciation resulting from polyploidy; autopolyploidy (same species) or
                               allopolyploidy (different species)
Isolating mechanism            Any mechanism that prevents interbreeding of hybrids.
Polyploidy                     When cells have more than 2n chromosomes. Polyploidy is common in
                               plants.
Pre-zygotic Isolation          Factors that prevent a hybrid from being conceived – includes behaviour,
                               structure, temporal (time), gamete incompatibility, geographical.
Post-zygotic Isolation         Factors that prevent a hybrid persisting as a new species – includes hybrid
                               inviability, hybrid infertility and hybrid breakdown.
Punctuated                     Pattern of evolution that consists of long periods of stability, followed by
equilibrium                    rapid changes as a result of critical selection pressures.
Selection pressure             The environmental factors that favour certain phenotypes.
Sequential Evolution           Pattern of evolution where a species changes over time to form a single
                               new species.
Speciation                     A mechanism by which new species are formed.
Species                        A group of individuals with common features and ancestry that will
                               interbreed in nature to produce fertile offspring.
Stabilising selection          Selection for the middle range against the extremes.
Subspecies                     Groups that are very different from each other, but can still interbreed.
                               Subspecies develop from races, but the differences are more extreme.
Sympatric                      Type of speciation occurring in the same area. There are a number of niches
                               and groups move into the niches best suited to them.