Forces of Evolution, Evolution in Action

Hardy-Weinberg principle

under certain assumptions (infinitely large population, random mating) both the frequencies of alleles, as well as the frequencies of genotypes (which are simply combinations of alleles), will remain constant from generation to generation. It then goes on to state what those frequencies are.

genetic drift

in small populations, random processes affect variation

• changes in allele frequencies due to change

• removes genetic variation

consequences of genetic drift

• produces random patterns of change

• causes differences to arise between small populations

mutation vs genetic drift

they have opposing influences on total genetic variation

• mutation adds and genetic drift removes

founder effect

• apart of genetic drift

  • a loss of variation that happens when a new population is started by a very small number of individuals by a parent group

    • may not have parent population because they may have differed in something so allelic frequencies may differ

genetic bottleneck

• apart of genetic drift

  • processes that have greater affects on smaller populations

  • something bad happens, population goes very low

  • a sharp, random reduction in size in population that severely limits genetic diversity

gene flow

movement of genes between populations

• can lead to evolution

What does gene flow do to between-group genetic variation

gene flow decreases between-group genetic variation

correlated characters

one reason why we might observe traits that appear to be maladaptive

• traits that tend to evolve or occur together in organisms because they share an underlying genetic pathway

pleiotropy is when…

correlations arise

when traits are correlated…

selection on one trait affects both

disequilibrium

another reason why we might observe traits that appear to be maladaptive

• natural selection only produces adaptations at equilibrium

at equilibrium populations will be stable

• change in any direction will be disadvantageous

• evolution will maintain status quo

• if change is fast and recent, populations won’t be well-adapted