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Natural Selection

Natural Selection. Developed by Charles Darwin in 1859 Mechanism by which better adapted organisms survive to produce a greater number of viable offspring Improve chances of survival Variation Individuals in a population vary in phenotype which also means their genotype

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Natural Selection

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  1. Natural Selection • Developed by Charles Darwinin 1859 • Mechanism by which better adapted organisms survive to produce a greater number of viable offspring • Improve chances of survival • Variation • Individuals in a population vary in phenotype which also means their genotype • Some variations are better suited for survival and are inherited • Overproduction • Populations tend to produce more offspring than are needed

  2. Neo-Darwinism • Refined version Darwin’s theory • Combines Mendel’s genetics • Evolution is driven by chance • 2 ways • Small scale mutations (single nucleotide polymorphisms) • Large scale mutations (recombination) • Creates new DNA by lucky accidents

  3. Gene Pools • Total genetic information (alleles) in the gametes of all individuals in any given population

  4. Population • Group of organism’s of one species that interbreed and live in the same place at the same time

  5. Factors that Affect Gene Pools • Mutation • Emigration • Geographical Barriers • Non-Random Mating • Genetic Drift • Bottleneck effect, founder effect • Gene Migration • Speciation • Selection Pressure • Adaptive Radiation

  6. Factors Contribute to Fitness of Individual • Fitness • Measure of how well suited an organism is to survive in its habitat and its ability to maximize the numbers of offspring surviving to reproductive age • How successful an organism is at passing on its genes • Natural selection tends to lean towards individuals who have specific traits that favour them in the environment

  7. Allele Frequency (Gene Frequency) • Proportion of a particular allele (variant of a gene) among all allele copies in a specific gene pool • Hardy-Weinberg principle is used to determine allele frequency: • p² + 2pq + q² = 1 • “p” and “q” represent frequency of alleles • “p” added to “q” always equals one (100%)

  8. Mutation • Random occurrences which change the genome of the organism • Increase genetic diversity • Advantageous mutations are favoured by natural selection • Disadvantageous mutations are phased out

  9. Geographical Barriers • Isolates the gene pool and prevents regular gene flow between populations

  10. Non-Random Mating • Members of gene pool seek out particular phenotypes increasing frequency of particular alleles • Decreases genetic diversity • Also known as selective breeding • Humans breed livestock and plants for particular traits (favourable) • Can lead to in-breeding depression caused by deleterious recessive alleles (cause abnormalities or death)

  11. Genetic Drift • Species of same population split into groups • Geographical barriers do not allow members of same gene pool to reproduce with one another increasing genetic diversity • Founder Effect • New population is started by few members of original population • Contains reduced genetic variation • Non-random samples of genes • Bottleneck Effect • Population size is reduced for at least one generation • Reduces genetic variation

  12. Gene Migration • Immigration • Populations gain alleles from other gene pools • Dependent on difference in allele frequencies between gene pools • Gene Flow • Members from one gene pool mate with members of another gene pool leading to alteration of allele frequencies • Emigration • Population loses alleles from gene pool

  13. Speciation • Genetic variation among population is so different that members can no longer reproduce with one another • New species is formed

  14. Selective Pressure • Environmental factors reducing reproductive success among members of a population • Contribute to evolutionary change or extinction through process of natural selection • Include • Competition, predation, disease, parasitism, land clearance, climate change, pollutants

  15. Antibiotic Resistant Bacteria • Microorganisms show resistance to an antimicrobial drug that was originally effective for treatment • Conjugation • Transfer of genetic material between bacterial cells • Creates genetic diversity • Antibiotic resistance

  16. Adaptive Radiation • Species from a common ancestor have successfully adapted to their environment via natural selection • Less competition in population • New ecological niches established (organisms function in environment) • Darwin’s finches

  17. Types of Natural Selection • Occur with or without environmental change • Effect a population • Stabilizing Selection • Constant environment • Maintain status quo • Directional Selection • New variation arises in constant environment • Disruptive Selection • Changing environment • Variations that result in better fitness in environment are favoured

  18. Stabilizing Selection • Favours the average individuals in a gene pool • Selects against extreme phenotypes of gene pool • Favours majority of population in gene pool • Diversity is decreased • Human birth weight • Infants with average birth weight have increased chance of survival

  19. Directional Selection • Favours one extreme phenotype over another extreme phenotype • Phenomena is observed in environments that have changed over time (climate change, food availability) • Population bell curve shifts to left or right • Fewer average individuals when compared to stabilizing selection • Beak length of Galapagos finches • Influenced by human interaction (hunting)

  20. Disruptive Selection • Average individual in a population is not favoured • Extreme phenotypes are observed • Lead to speciation (new species) • Diversity increased • Influence by human interaction (environmental pollution) • London’s peppered moths

  21. Sexual Selection • Special case of natural selection • An organism’s ability to successfully copulate with a mate • Usually female chooses among males • 2 ways • Female choice • Male competition

  22. Female Choice • Intersexual selection between sexes • Females choose males based on specific characteristics or behaviours

  23. Male Competition • Intrasexual selection • Males compete against other males for territory or mating rights with females • Lead to intense battles

  24. Evidence of Evolution • Fossil record of change in earlier species • DNA/protein homologies • Geographic distribution of related species • Recorded genetic changes in living organisms over many generations

  25. DNA/Protein Homologies • All living things on earth share the ability to create complex molecules out of carbon and a few other elements • All plants and animals inherit their specific characteristics from a combination of genes • Protein is made from DNA made up mostly of only 20 kinds of amino acids

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