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Evolution Unit

Explore the concept of evolution, including genetic variations and natural selection. Learn about the mechanisms that drive evolutionary change and the impact of human activities on genetic diversity. Discover evidence supporting evolution, including the fossil record and comparative anatomy.

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Evolution Unit

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  1. EvolutionUnit

  2. 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

  3. Genetic variation in a population

  4. 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

  5. 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

  6. 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, speciationoccurs • Thus, the frequency change is NOT RANDOM

  7. Effects of Selection • Changes in the average trait of a population DIRECTIONALSELECTION STABILIZINGSELECTION DISRUPTIVESELECTION giraffe neck horse size rock pocket mice human birth weight

  8. Natural selection in action Resistance… NOT immunity! MRSA

  9. Hidden variations can be exposed through selection! Terminal bud Cabbage Brussels sprouts Artificial selection Lateral buds Leaves Flower cluster Kale Cauliflower Stem Flower and stems Kohlrabi Wild mustard Broccoli

  10. In addition to natural selection, evolutionary change is also driven by random processes…

  11. 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

  12. 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

  13. Peregrine Falcon 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 Golden Lion Tamarin

  14. 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

  15. 2006 Fossil Discovery of Early Tetrapod “Tiktaalik” “missing link” from sea to land animals Evidence Supporting Evolution

  16. 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 • Homologousstructures– body parts with similar structure but possible different function. Shows common ancestry • Analogousstructures– similar structure develops in organisms that share a common ecosystem but not a common ancestry • Biochemical or Molecular • Similarities in gene sequences, proteins, DNA

  17. 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

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

  19. 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: C14 decays into N14

  20. Relative Dating

  21. Homologous Structures Anatomical evidence

  22. Analogous structures Don’t be fooledby their looks! Convergent evolution Those fins & tails & sleek bodies areanalogous structures! Does this mean they have a recent common ancestor? Solving a similar problem with a similar solution

  23. These areremnants ofstructures that werefunctional inancestral species Vestigial organs Why would whaleshave pelvis & leg bonesif they were alwayssecreatures?

  24. Coevolution • Two or more species reciprocally affect each other’s evolution • predator-prey • disease & host • competitive species • mutualism • pollinators & flowers

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