Natural Selection

Natural selection -

  • selects for traits that are present ,

  • acts on phenotypes not genotypes

  • acts on quantitative (numerical) values in many different ways

    3 ways

  • Stabilizing - averages

  • Directional - selecting for one extreme (positive)

  • Disruptive - selects for opposite extremes (causes variation)

  • Genetic drift - random changes in allele frequencies from one generation to another

  • Population bottleneck - an environmental event resulting in survival of only a few individuals (decreases genetic drift dramatically) - (Noah’s ark)

  • Founder effect - genetic drift changes allele frequencies when a few individuals colonize an area

Mutation -

  • creates new traits

  • random changes in DNA

Evolution -

  • happens within a population

  • Occurs when allele frequency changes

Genetic variation -

  • meiosis

  • environmental chemicals,

  • replication mistakes

Speciation -

  • forms new biological species (usually by the division of a single species into two or more genetically distinct one)

    Different isolations -

  • Mechanical isolation- mating doesn’t structurally work, gametes wont fuse

  • behavioral isolation - ex. birdsongs

  • Temporal - two or more species reproduce at different times

  • Postzygotic isolating mechanisms - hybrids offsprings can’t either reproduce or develop