7.5 - genetic drift, gene flow and speciation

genetic drift

evolutionary change due to random chance, not fitness

reduces variation

more pronounced in small pops

pop bottleneck

occurs after catastrophic events drastically reduce pop size

allele frequencies change randomly

founder effect

subset of a pop colonizes a new area

allele frequencies differ from original pop

gene flow

movement of genes/alleles between pops (migration)

increases genetic variation

reduces differences between pops

impact of gene flow

high - pops blend - reduce divergence

affects adaption (ex. pesticide resistence in beetles)

important for pop survival and reducing extinction risk

biological species concept

group that can interbreed and produce viable, fertile offspring

repro isolation is key

morphological species concept

classifies species based on form and structure

used for fossils and asexually reproducing organisms

subjective

prezygotic barriers

prevent fertilization

habitat iso (prezygotic)

species live In different habitats

behavorial iso (prezygotic)

different courtship behaviors

temporal behaviors (prezygotic)

different mating seasons/times

mechanical iso (prezygotic)

incompatible repro anatomy

gametic iso (prezygotic)

gametes cant fuse

postzygotic barriers

after fertilization

zygote mortality (postzygotic)

zygote fails to develop

hybrid sterility (postzygotic)

offspring is sterile

hybrid breakdown (postzygotic)

F1 hybrids are fertile, but F2 generations have reduced fitness

allopatric speciation - “other country”

geographic barrier prevents gene flow

ex. rivers, mountains, etc

most common speciation

sympatric speciation - “same country”

occurs without physical barrier - behavioral or ecological differences

ex. penguins with different mating behaviors