Origins of Life 2 - Mechanisms


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Natural Selection

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  • Hardy-Weinberg Equilibrium = p 2 + pq + q 2 = 1
  • Substitution A substitution is a mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G). Such a substitution could: change a codon to one that encodes a different amino acid and cause a small change in the protein produced. For example, sickle cell anemia is caused by a substitution in the beta-hemoglobin gene, which alters a single amino acid in the protein produced. change a codon to one that encodes the same amino acid and causes no change in the protein produced. These are called silent mutations. change an amino-acid-coding codon to a single "stop" codon and cause an incomplete protein. This can have serious effects since the incomplete protein probably won't function. Insertion Insertions are mutations in which extra base pairs are inserted into a new place in the DNA. Deletion Deletions are mutations in which a section of DNA is lost, or deleted. Frameshift Since protein-coding DNA is divided into codons three bases long, insertions and deletions can alter a gene so that its message is no longer correctly parsed. These changes are called frameshifts. For example, consider the sentence, "The fat cat sat." Each word represents a codon. If we delete the first letter and parse the sentence in the same way, it doesn't make sense. In frameshifts, a similar error occurs at the DNA level, causing the codons to be parsed incorrectly. This usually generates truncated proteins that are as useless as "hef atc ats at" is uninformative. There are other types of mutations as well, but this short list should give you an idea of the possibilities.
  • Six-legged frog - genetic mutation.
  • Both interact with the environment the organism lives in, but both are not adaptations.
  • Peppered moth changing color due to adaptation to England’s industrial revolution resulting in blackened tree bark. Kettlewell's experiments were flawed (moths released at wrong time of day, and in numbers creating a possible predatory magnet of the birds). Moths rest not on tree trunks, but under leaves, higher up in the tree canopy. Even so, as the environment changed, so did the phenotypic predominance of the darker species, showing a great example of adaptation (but not evolution). "Industrial melanism"
  • Species A migrates from the mainland to the first island. Isolated from the mainland, species A evolves to species B. Species B migrates to the second island. Species B evolves in species C. Species C recolonizes the first islands, but is now unable to reproduce with species B. Species C migrates to the third island. Species C evolves into species D. Species D migrates to the first and second island. Species D evolves to species E.
  • i.e. bugs get stepped on, fire wipes out certain plants, etc.
  • Origins of Life 2 - Mechanisms

    1. 1. Origins of Life Mechanisms of Evolution - Natural Selection -
    2. 2. What is Evolution? Simple: "change over time"  Less Simple: "descent with modification" • many, many, MANY small changes over LOOOOOOOOONG periods of time that result in the formation of many DIFFERENT types of organisms
    3. 3. Descent with Modification Given enough time, many small changes could add up to big changes within populations of organisms Mechanisms of change: • mutation • migration • natural selection • genetic drift Requires a very, very, very, very, VERY long time to happen
    4. 4. Gene Frequency Evolution occurs when there is a change in gene frequency within a population over time. • Gene frequency: the percentage of a particular allele compared to the total of all other alleles of the same gene in a given population
    5. 5. Mutations A mutation is a change in DNA sequence that alters the trait a specific gene controls • Only one nucleotide pair in a thousand is randomly changed every 200,000 years • Some genes control many traits or affect the expression of many other genes Caused by: • Copying errors in the genetic material during cell division  Deletion  Insertion  Translocation • Increased by exposure to ultraviolet or ionizing radiation (x-rays), chemical mutagens, or viruses
    6. 6. Results of Mutation Results: • most mutations are neutral  have no effect on survival/reproduction • many are harmful  detrimental to fitness or lethal • VERY small percent are advantageous  result in a change in phenotype that improves reproductive success Cell type matters: • germ cell (reproductive/sex cell) mutations are passed on to offspring • DNA of somatic cells arent passed to offspring (mutations stay local)
    7. 7. What Changes are Passed On? Inherited Traits: • characteristics determined by genes (DNA)  eye color, height, tongue- rolling ability  NOT Environmental/Learned Traits: • things your circumstances teach you  language, how to play piano, love of cheese
    8. 8. Adaptations "Fitness" = an organisms ability Adaptations are inherited to survive and reproduce traits that improve help an organism survive and reproduce • "I was born with rugged good looks and easily found a wife, even though there were very few women in the Jamestown colony."  Adaptations are NOT learned behaviors or characteristics • "Our family moved to the Alaska and eventually adapted to the climate."
    9. 9. Adaptation & Environment A given trait may or may not be an adaptation, depending on the environment in which the organism lives. Would these cats long fur be an adaptation in... Sahara Desert? Alaska?
    10. 10. Gene Flow Gene flow occurs when organisms migrate - new genes are introduced when an organism travels to join a different population - only creates change when populations are isolated • geographically or • reproductively
    11. 11. Natural Selection A mutation may improve "fitness" (chance of survival/reproduction) • competition for resources • health/hardiness • reproductive success • predator evasion Only the fittest (best adapted to survival) can reproduce Traits passed on are those with best adaptations to the current environment
    12. 12. Case Study White Peppered Moth populations dwindled and black phenotype flourished Assumed bird predation diminished the less-camouflaged white moths Individuals less adapted to their environment dwindle and may eventually become extinct  Experiment flaws: • variables not accounted for:  migration may have affected numbers  time of release, landing behavior, diet  the artificially high numbers released might have created a predatory magnet
    13. 13. Speciation in Darwin’s Finches In the 1830’s Darwin sailed around the world and observed incredible diversity in the population of finches on the Galapagos Islands
    14. 14. Galapagos Finch Migration  Natural selection occurred as the birds competed for food and resources.  Adaptations selected by new surroundings when they migrated from mainland to islands  Geographic and then reproductive isolation kept the species distinct
    15. 15. Genetic Drift Random changes in allele frequency • random circumstances cause an allele to become more common (or extinct) Freak Lawnmower Accident!  What if the mower-gone- crazy takes out all but two rose bushes, wiping out all the recessive alleles in a population?
    16. 16. Genetic Variation Evolutionary change cannot happen without a change in genes and gene combinations. Sources of variation: • Mutation • Gene Flow  genetic exchange due to the migration  without isolation, reduces differences between populations (acts against genetic variation) • Sexual Reproduction
    17. 17. Meiosis & Genetic Variation Sexual Reproduction increases genetic variation • Crossing Over  segments of DNA swap places during prophase 1 of meiosis • Independent Assortment  chromosomes line up randomly during meiosis
    18. 18. Types of Evolution Microevolution • small changes within a species set of genes that result in phenotypic differences • hundreds of years (short time) Macroevolution • descent with modification • the process by which modern organisms have descended from ancient ancestors due to many small changes over hundreds of thousands of years (long time)
    19. 19. Speciation a lineage-splitting event that produces two or more separate species is called speciation • produced in lab experiments • populations change so much that they no longer can interbreed and exchange genes • seems to require geographic isolation Macroevolution = speciation on steroids Individuals DO NOT evolve over time. ...but POPULATIONS do!
    20. 20. CoevolutionEvolution in which two different species affect each others adaptations.Occurs between organisms that have close ecological relationships: • Competitive  fight each other for limited resources • Mutualistic  live together in a way that helps them both survive easier • Predator/prey  one hunts/eats the other as food • Parasite/host  one lives off the other, without killing it completely