| A | B |
|---|
| allele | alternate form of a gene (slightly different base sequences) |
| bottleneck effect | when a population's size is reduced for at least one generation |
| founder effect | a severe type of bottleneck where the whole population is descended from a small number of individuals |
| mitochondrial DNA | found in the mitochondria, so only passed on from the mother (only eggs contain mitochondria) |
| divergent evolution | two or more species that have a common ancestor have undergone this |
| convergent evolution | species NOT closely related develop similar traits due to inhabiting similar niches |
| natural selection | process: individuals (and their alleles) are more likely to survive and reproduce if alleles are beneficial in current environment |
| analogous structures | same function, different origins |
| homologous structures | related structures, common ancestor, function can be lost or altered |
| niche | habitat + behaviours/interactions |
| non-disjunction | failure of one or more (or all) homologous chromosome pairs to separate during meiosis |
| polyploidy | cells or organisms with more than two sets of chromosomes |
| diploid gametes | these can be formed during meiosis if non-disjunction occurs |
| speciation | the formation of new species: when organisms diverge enough that fertile young are no longer possible between them |
| directional selection | where one of the extremes in the population is selected for |
| stabilising selection | an average/middle/non-extreme phenotype is favoured/selected for |
| diversifying selection | two or more extremes of phenotype are selected for |
| reproductive isolating mechanisms | behaviours or physiological factors that prevent fertile offspring (or any offspring) being produced |
| allopatric speciation | speciation as the result of geograhical separation |
| sympatric speciation | speciation that has taken place without geographical separation |
