selection and speciation Flashcards
describe natural selection
individuals vary/mutations take place
some are better adapted for survival- more likely to reproduce and pass on alleles
over time frequency of advantageous allele increases in the population
whats directional selection
when there is an environmental change. selective pressures for species to change in response to it
favours individuals that are phenotypically different
whats stabilising selection
no change in environment it remains stable
individuals with phenotype closest to mean selected for. individuals with extreme phenotypes selected against which reduces them distribution curves become narrower
describe speciation
results in evolution of new species from an existing one. usually the result of geographic isolation which is when one population becomes separated into 2 by geographical barrier
2 gene pools cannot mix
populations face different selective pressures as have different environmental conditions - adapted organisms survive and breed
selection for specific alleles over a long period of time
allelic frequency changes
eventually becomes so different that theyre different species who can no longer interbreed to produce fertile off spring
define species
a group of individuals with similar genes that are able to breed with each other to produce fertile offspring
define gene pool
all the alleles in a population
whats disruptive selection
favours extreme phenotypes and selects for them whilst intermediate values are selected against. environmental factor takes two distinct forms
whats allopatric speciation
describes the type of speciation where two populations become geographically isolated
physical barrier
whats sympatric speciation
reproductively isolated. same population then mutation causes different alleles. reproductive separation as no gene flow - gene pools remain separate. different alleles passed on/ change in frequency of alleles in population
form of disruptive selection
