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Evolution of Populations

Explore how mutation creates genetic variation, gene flow influences genetic mixing, non-random mating impacts populations, and genetic drift leads to allele frequency changes over time.

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Evolution of Populations

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  1. Evolution of Populations

  2. Warm Up- 1/22 • How do you think migration affects genetics?

  3. Good Things

  4. Challenge • Basketball Ticket Raffle • Behavior • Academics • This Saturday! • Drawing on Friday

  5. Lab Update

  6. Populations evolve • Natural selection acts on individuals • differential survival • “survival of the fittest” • differential reproductive success • who bears more offspring • Populations evolve • genetic makeup of population changes over time • favorable traits (greater fitness) become more common Presence of lactate dehydrogenase Mummichog

  7. Body size & egg laying in water striders Fitness • Survival & Reproductive success • individuals with one phenotype leave more surviving offspring

  8. Variation & natural selection • Variation is the raw material for natural selection • there have to be differences within population • some individuals must be more fit than others

  9. Wet year Beak depth Dry year Dry year Dry year 1977 1980 1982 1984 11 10 Beak depth of offspring (mm) 9 Medium ground finch 8 8 9 10 11 Mean beak depth of parents (mm) Where does Variation come from? • Mutation • random changes to DNA • errors in mitosis & meiosis • environmental damage • Sex • mixing of alleles • recombination of alleles • new arrangements in every offspring • new combinations = new phenotypes • spreads variation • offspring inherit traits from parent

  10. Mutation Gene Flow Non-random mating Genetic Drift Selection Title: Types of Evolutionary Change

  11. 1. Mutation & Variation • Mutation creates variation • Mutation changes DNA sequence, changes amino acid sequence, and changes proteins.

  12. 2. Gene Flow • Movement of individuals and their alleles in & out of populations • Causes genetic mixingacross regions • seed & pollen distribution by wind & insect • migration of animals • sub-populations may have different allele frequencies • reduce differences between populations

  13. Gene Flow Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.

  14. Human evolution today • Gene flow in human populations is increasing today • transferring alleles between populations Are we moving towards a blended world?

  15. 3. Non-random mating • Sexual selection • Organisms may prefer to mate with others of the same genotype or of different genotypes.

  16. Warbler finch Tree finches Ground finches 4. Genetic drift • Effect of chance events • founder effect • small group splinters off & starts a new colony • bottleneck • some factor (disaster) reduces population to small number & then population recovers & expands again

  17. 4. Genetic drift • Founder Effect- When a new population is started by only a few individuals. • some rare alleles may be at high frequency; others may be missing • skew the gene pool of new population • human populations that started from small group of colonists • example: colonization of New World

  18. Distribution of blood types • Distribution of the O type blood allele in native populations of the world reflects original settlement

  19. Distribution of blood types • Distribution of the B type blood allele in native populations of the world reflects original migration

  20. Out of Africa Likely migration paths of humans out of Africa 10-20,000ya 10-20,000ya 50,000ya Many patterns of human traits reflect this migration

  21. 4. Genetic drift • Bottleneck Effect- When large population is drastically reduced by a disaster and lowers variation. Also narrows the gene pool. • famine, natural disaster, loss of habitat… • loss of variation by chance event • alleles lost from gene pool • not due to fitness

  22. 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

  23. 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

  24. Warm Up- 1/23 • What evolution affect deals with a natural disaster or tragic event killing off the majority of a population?

  25. Good Things

  26. 5. Natural selection • Survival & reproduction due to changing environmental conditions. • climate change • food source availability • predators, parasites, diseases • toxins • combinations of allelesthat provide “fitness” increase in the population • adaptive evolutionary change

  27. 5. Natural Selection • Directional Selection- one extreme trait is favored over the others, causing the organism to be more fit and have more offspring that survive. • An example of this is running speed in rabbits. The faster rabbits can outrun predators easier, so they are less likely to get eaten, and more likely to survive and produce offspring. Directional selection favors the trait of fast running.

  28. 5. Natural Selection • Stabilizing Selection- the traits that are the most average are selected for, and the extremes are selected against. • One example of a trait that has experienced stabilizing selection is birth weight. Babies that are very small are often not healthy enough to survive, while babies that are too large may get stuck in the birth canal, causing death of the baby and frequently death of the mother as well.

  29. 5. Natural Selection • Disruptive Selection- the extreme traits are selected for, and average traits are selected against. • One example of this is beak sizes in birds. If the only seeds available in an environment are small seeds and large seeds, natural selection will favor birds with either small or large beaks. The birds with medium sized beaks will not be very effective at feeding, so medium beaks will be selected against.

  30. Warm Up- 1/24 • A giant mountain separates two types of squirrel. Is this a Temporal Isolation, Geographic Isolation, or Behavioral Isolation?

  31. Good Things

  32. CFA • Bit.ly/HISDAssessments

  33. Peppered Moth Lab

  34. Mutation Gene Flow Non-random mating Genetic Drift Selection 5 Agents of evolutionary change

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