AP Biology Evolution Unit

What is Evolution? Change in the genetic makeup of a population over time. Fitness – those with favorable variations for survival and reproduction. – Populations can evolve, not individuals. Diverse gene pool good for long-term survival of a species. Genetic variations are important! How do genetic variations occur? – Mutation, sexual reproduction, artificial selection, genetic technology

Genetic variation in a population

AP Biology Essence of Darwin’s ideas  Natural selection  heritable variation exists in populations  over-production of offspring  more offspring than the environment can support  competition  for food, mates, nesting sites, escape predators  differential survival  successful traits = adaptations  differential reproduction  adaptations become more common in population

AP Biology Lamarckian vs. Darwinian view  LaMarck  in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring  Darwin  giraffes born with longer necks survive better & leave more offspring who inherit their long necks

Natural Selection Major mechanism of evolution Environment is always changing Acts upon the phenotype of the population Based on Darwin’s idea that resources are limited and that there is competition for those resources. Adaptation = a genetic variation favored by natural selection. When allele frequencies shift, speciation occurs – Thus, the frequency change is NOT RANDOM

AP Biology Effects of Selection  Changes in the average trait of a population DIRECTIONAL SELECTION STABILIZING SELECTION DISRUPTIVE SELECTION giraffe neck horse size human birth weight rock pocket mice

AP Biology Natural selection in action MRSA Resistance… NOT immunity !

AP Biology Hidden variations can be exposed through selection! Terminal bud Lateral buds Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Flower and stems BroccoliWild mustard Kohlrabi Stem Kale Artificial selection

AP Biology In addition to natural selection, evolutionary change is also driven by random processes…

AP Biology Genetic Drift  Chance events changing frequency of traits in a population  not adaptation to environmental conditions  not selection  founder effect  small group splinters off & starts a new colony  it’s random who joins the group  bottleneck  a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool  who survives disaster may be random

AP Biology Ex: Cheetahs  All cheetahs share a small number of alleles  less than 1% diversity  as if all cheetahs are identical twins  2 bottlenecks  10,000 years ago  Ice Age  last 100 years  poaching & loss of habitat

AP Biology Conservation issues  Bottlenecking is an important concept in conservation biology of endangered species  loss of alleles from gene pool  reduces variation  reduces adaptability Breeding programs must consciously outcross Peregrine Falcon Golden Lion Tamarin

AP Biology Human Impact on variation  How do we affect variation in other populations?  Artificial selection/Inbreeding  Animal breeds  Loss of genetic diversity  Insecticide usage  Overuse of antibiotics  resistant bacterial strains

AP Biology Evidence Supporting Evolution 2006 Fossil Discovery of Early Tetrapod “Tiktaalik” “missing link” from sea to land animals

AP Biology Evidence for Evolution Paleontology – fossils show change in a species over time Biogeography – Similar species are found in similar ecosystems around the world Morphology – Comparing structures – Homologous structures – body parts with similar structure but possible different function. Shows common ancestry – Analogous structures – similar structure develops in organisms that share a common ecosystem but not a common ancestry Biochemical or Molecular – Similarities in gene sequences, proteins, DNA

AP Biology Fossils  Preserved remains of living things  Paleontology is the study of the fossil record  Most organisms do not leave a fossil after death  Explains the “missing links”  Sedimentation Fossils  As the organism decomposes the spaces will be filled with the minerals from the silt

AP Biology The Archaeopteryx Fossil Avian Features Vertebrae are almost flat- faced. Impressions of feathers attached to the forelimb. Belly ribs. Incomplete fusion of the lower leg bones. Impressions of feathers attached to the tail. Forelimb has three functional fingers with grasping claws. Reptilian Features Lacks the reductions and fusions present in other birds. Breastbone is small and lacks a keel. True teeth set in sockets in the jaws. The hind-limb girdle is typical of dinosaurs, although modified. Long, bony tail. LEFT: Archaeopteryx lithographica Found in 1877 near Blumenberg, Germany

AP Biology How old is that fossil?  Relative Dating  Age of fossils based according to their location in strata  Absolute Dating  Age of fossils determined by analyzing the content of radioactive isotopes found in the fossil.  Half-life: The length of time required for half of the radioactive elements to change into another stable element.  Unaffected by temperature, light, pressure, etc.  All radioactive isotopes have a dependable half life. Ex: C 14 decays into N 14

AP Biology Relative Dating

AP Biology Anatomical evidence Homologous Structures

AP Biology Analogous structures Solving a similar problem with a similar solution Does this mean they have a recent common ancestor? Don’t be fooled by their looks! Those fins & tails & sleek bodies are analogous structures! Convergent evolution

AP Biology Vestigial organs Why would whales have pelvis & leg bones if they were always secreatures? These are remnants of structures that were functional in ancestral species

AP Biology Coevolution  Two or more species reciprocally affect each other’s evolution  predator-prey  disease & host  competitive species  mutualism  pollinators & flowers