ap/ib biology- evolution

evolution

change in allele frequencies in a population over time

• happens at the population level, not individuals

• driven by genetic variation and environmental pressures

allele frequency

how common an allele is in a population

natural selection

individuals with advantageous traits

gene pool

all alleles in a population

fitness

reproductive success

adaptation

inherited trait that increases survival

speciation

formation of new species

genetic drift

random changes in allele frequency

gene flow

movement of alleles between populations

mutation

random change in DNA

artificial selection

humans selecting traits

directional selection

1 extreme trait is favored

stabilizing selection

• average phenotype favored

• reduces variation

• ex: human birth weight

disruptive selection

• both extremes favored

• can lead to speciation

fossil records

• shows changes over time

• transitional fossils = links between species

molecular evidence

• DNA similarities = common ancestry

• more similar DNA → more closely related

homologous structure

same structure, different function (common ancestor)

analogous structure

different structure, same function

vestigial structure

no longer useful (ex: appendix)

mutation

• primary source of variation

• random, creates new alleles

genetic drift

• strong in small populations

• ex: bottleneck effect → sudden population reduction (those who survived)

• ex: founder effect → small group starts new population

gene flow

• movement of alleles between populations

• increases variation

natural selection

• non random

• environment selects traits

hardy-weinburg equilibrium

• p + q = 1

• p² + 2pq + q² = 1

allopatric speciation

geographic barrier separates populations

sympatric speciation

• no physical barrier

• often due to behavior differences/plants

prezygotic barriers (before fertilization)

• temporal (different mating times)

• behavioral

• mechanical

postzygotic barriers

hybrid is weak/sterile

divergent evolution

species become more different

covergent evolution

unrelated species become similar

co-evolution

species evolve together

microevolution

change in allele frequencies over time or generations