selection and evolution

genetic variation

differences between the dna base sequence of individuals within a species

phenotypic variation

differences between the observable characteristics of individuals within a species

discontinuous variation

differences between individuals of a species in which each one belongs to one of a small number of distinct categories, with no intermediates

continuous variation

differences between individuals of a species in which each one can be at any point in the range between the highest and lowest values

polygenes

number of different genes at different loci that all contribute to a particular aspect of a phenotype

environmental facotr

feature of the environment of an organism that affects its survival

biotic factor

an environmental factor that is caused by living organisms (eg predation, competition)

competition

the need for a resource by two organisms, when that resource is in short supply

abiotic factor

environmental factor that is caused by nonliving components eg soil pH, light intensity

fitness

ability of an organism to survive and reproduce

selection pressure

an environmental factor that affects the chance of survival of an organism, organisms with one phenotype are more likely to survive and reproduce than those with a different phenotype

natural selection

process by which individuals with a particular set of alleles are more likely to survive and reproduce than those with other alleles. over time and generations, the advantageous alleles become more frequent in the population

stabilising selection

natural selection that tends to keep allele frequencies relatively constant over many generations

directional selection

natural selection that causes gradual change in allele frequency over many generations

disruptive selection

natural selection that maintains relatively high frequencies of two different sets of alleles. individuals with intermediate features and allele sets are not selected for

polymorphism

continued existence of two or more different phenotypes in a species

genetic drift

gradual change in allele frequencies in a small population, where some alleles are lost or favoured just by chance and not by natural selection

gene pool

the complete range of dna base sequences in all the organisms in a species or population

founder effect

reduction in a gene pool compared with the main populations of a species, resulting from only two or three individuals (with only a selection of the alleles in the gene pool) starting off a new population

evolutionary bottleneck

a period where the numbers of a species fall to a very low level, resulting in the loss of a large number of alleles and therefore a reduction in gene poll of the species

artificial selection

selection by humans of organisms with desired traits to survive and reproduce; also known as selective breeding

inbreeding depression

loss of ability to survive and grow well, due to breeding between close relatives. this increases the chance of harmful recessive alleles coming together in an individual and being expressed

inbreeding

breeding between organisms with similar genotypes, or that are closely related

outbreeding

breeding between individuals that are not closely related

hybrid vigour

increased ability to survive and grow well as a result of outbreeding and therefore increased heterozygosity

evolution

process leading to formation of new species from pre existing species over time

morphological

relating to structural features

physiological

relating to metabolic and other processes in a living organism

reproductive isolation

inability of two groups of organisms to breed with one another. two populations of the same species may be geographically separated or two different species are unable to breed to produce fertile offspring

genetically isolated

no longer able to breed together, there is no exchange of genes

speciation

production of new species

geographical isolation

separation by a geographical barrier, eg stretch of water or mountain range

allopatric speciation

development of new species following geographical isolation

sympatric speciation

development of new species without any geographical isolation

ecological separation

separation of two populations because they live in different environments in the same area and so cannot breed together

behavioural separation

separation of two populations because they have different behaviours which prevent them breeding together