BIOL1020 - Week 8.2

mechanisms of evolution

• natural selection

• genetic drift (random)

• gene flow (movement of alleles between pops.)

• mutation (creates new alleles)

adaptive evolution

• population becomes better suited to their environment

• individuals with beneficial traits survive/reproduce more

malthus’ principle

• more individuals are born than can survive

• limited resources are up for competition

phenotypic variation

• traits vary among individuals in a population

  • morphology

  • physiology

  • behaviour

differential fitness

• individuals have different survival and reproduction rates

• some leave more offspring than others

hertability

traits can be passed from parents to offspring

• based on genes

results of natural selection

• changes in allele frequencies over time → evolution

• increase in average fitness → adaptive evolution

directional, disruptive, stabilizing, and natural selection

• directional: favours individuals at one extreme

• disruptive: favours individuals at both extremes

• stabilizing: favours intermediate phenotypes

• natural: differences in lifetime reproductive success among phenotypes

survival of the fittest

• survival only matters if it leads to reproduction

sexual selection

• selection for mating success

• can produce sexual dimorphism

  • differences between males and females

intrasexual and intersexual selection

• intra: competition within the same sex

• inter: one sex chooses mates

genetic drift

• random change in allele frequencies

• cna increase or decrease randomly

fixation

one allele becomes the only allele at a locus

genetic drift in small vs. large populations

• small: rapid allele frequeny changes

• large: slower, less extreme changes

difference between genetic drift and natural seelction

genetic: random, non-adaptive

natural: non-random, adaptive

bottleneck effect

• rapid reduction in population size due to external pressures

• causes over-hunting, habitat loss, natural disasters

• loss of genetic variation, altered allele frequencies

founder effect

• small group starts a new population

• not genetically representative of original population

• loss of genetic variation, different allele frequencies

gene flow

• introduces new alleles

• reduces differences between populations

• makes populations more genetically similar

mutation and how it contributes to evolution

• random changes in DNA sequence

• creates entirely new alleles

• original source of genetic variation

• passed on in reproductive cells