Download Mechanisms of Evolution

Mechanisms of Evolution
15.2 Population Genetics
 Darwin did not know about genes
 Now we know more about how change happens
 Individuals don’t evolve
 Populations evolve
 Population = all members of a species that live in an area
 Each member has genes = alleles
 Evolution happens when genes in a population change over time
 Gene pool = all alleles in a population’s genes
 Allelic frequency = percentage of any one allele in the gene pool
 Genetic equilibrium = a population in which allele frequency stays the same over
generations
 Change in allele frequency = evolution
Things that change gene pool
 Mutation – chance, radiation, pollution
 Many mutations lethal, but sometimes beneficial
 Genetic drift – chance events
 Gene flow – migration – movement in and out of population
 Natural selection – some variations increase or decrease chance of survival
Direction of natural selection
 Stabilizing selection – favors average individual
 Directional – favors one extreme
 Disruptive – favors either extreme
15.2 Evolution of Species
How do changes in a gene pool lead to new species?
 Speciation = evolution of new species
 When members of similar populations no longer interbreed
 Things that cause speciation
 Geographic isolation – physical barrier divides population
 Reproductive isolation – formerly interbreeding groups can no longer mate
 Genetic
 Behavioral
 Change in chromosome number = polyploidy
 within species or hybridization between species
 Is speciation fast or slow?
 Gradualism – species originate from gradual change of adaptations
 Punctuated equilibrium – speciation happens in rapid bursts with long
periods of genetic equilibrium in between
Patterns of Evolution
 Adaptive radiation – ancestral species evolves into many species
 Divergent evolution – adaptive radiation leads to new species getting more
different
 Convergent evolution – organisms evolve similar traits because they live in
similar environments