Speciation (NBTS)

Adaptive radiation

When a large number of species form to occupy different ecological niches

Allopatry

Speciation as a result of geographical isolation

Allopatric speciation

Speciation occuring where organisms are initially capable of actually interbreeding but cannot because they are geographically seperated

analogous structures

structures which have the same function but have different bone makeup e.g. wings of birds, bats, and insects

biogeography

the study of the geographic distribution of organisms

cline

a gradual variation in the characteristics of a species or population or population over a geographical range

co-evolution

when one species or group changes its genetic composition in response to a genetic change in another

convergent evolution

when different specis living in the same environment come to look similar

divergent evolution

when one species branches to form two or three species

embryology

the study of how embryos develop, looking at which genes are turned on and when

endemic

only found naturally in a certain country or area

evolution

the gradual process by which the present diversity of plants and animals arose from the earliest and most primitive organisms

genetic drift

the important random fluctuation in the frequencies of alleles due to chance events

Geographic or topographic barrier

a physical barrier (for the species) that prevents gene flow e.g. mountain ridge

gradualism

slow changes between populations that occur as a result of different selective pressures

homologous structures

structures which have a similar evolutionary history but have developed to suit different functions e.g. wing of bat and flipper of dolphin

hybrid

an individual formed by a mating between genetically different populations or species

instant speciation

the formation of a new species through autopolyploid or allopolyploid. Because the chromosome numbers of the new ‘instant’ species do not match that of the original species they cannot interbreed

isolating mechanisms

any mechanism that prevents interbreeding of hybrids

parallel evolution

the development of related organisms along similar evolutionary paths due to strong selective pressures on all them in the same way

polyploidy

when cells have more than 2n chromosomes; common in plants

punctuated equilibrium

where evolution consists of long periods of stability, followed by short rapid changes as a result of critical selection pressures

reproductive isolation

a barrier to breeding that exists due to differences in mating seasons or mating organs e.g. flowers flowering at different times of the year

ring species

two apparently distinct species that are connected by a series of intermediate geographical and structural subspecies between which interbreeding can occur

selection pressure

the environmental factors that favour certain phenotypes

speciation

a mechanism by which new species are formed

species

a group of individuals with common features and ancestry, which will interbreed

sympatry

speciation within the same area by natural selection; there are a number of niches and groups move into the niches best suited to them

temporal barrier

when gene flow is prevented due to the populations or species having different mating times of day, month or year

vestigial organ

any part of an organism that has diminished in size during its evolution because the function it serves has decreased in importance e.g. the appendic in humans

mutation

Permanent change to the base sequence of DNA

natural selection

certain individuals are more likely to survive in an environment due to having more favourable phenotypes, causing a change in frequency of alleles

niche

the specific role an organism has in its environment

hybrid inviability

the fertilised egg may fail to develop properly

hybrid sterility

hybrid may be viable but sterile/infertile (cannot breed, e.g. mule)

hybrid breakdown

generation may be fertile but later generations inviable or infertile

Punctuated equilibriam

Long periods of stasis followed by rapid periods of evolution/speciation/allele change

polyploidy

meiosis does not occur properly so new individuals have more than diploid (2n) chromosomes

gradualism

small changes are collected in a population over time

directional evolution

one extreme phenotype favoured over median or other extremes

cline

a gradual variation in the characteristics of a species or population over a geographical range