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Unit 4- Evolution

Unit 4- Evolution. 8.1 Natural Selection. Overview of section. Types of selection Directional Stabilizing Disruptive Sexual Natural Evolutionary change without selection Genetic drift Genetic bottlenecks Founder effect. Types of selection: Directional.

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Unit 4- Evolution

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  1. Unit 4- Evolution 8.1 Natural Selection

  2. Overview of section • Types of selection • Directional • Stabilizing • Disruptive • Sexual • Natural • Evolutionary change without selection • Genetic drift • Genetic bottlenecks • Founder effect

  3. Types of selection: Directional • Selection that favours increase or decrease away from average phenotype http://avonapbio.pbworks.com/w/page/9429288/Ch-23

  4. Types of selection: Stabilizing • Selection when average phenotype is selected for. http://kenpitts.net/bio/evolution/selections/stabilize.html

  5. Types of selection: Disruptive • Selection that favours extreme individuals over those with average phenotype. http://www.sparknotes.com/biology/evolution/naturalselection/section1.html

  6. Types of selection: sexual • Selection that favours individuals with traits that increase their mating success.

  7. Sexual selection and evolution video http://www.youtube.com/watch?v=gKybAp--n7M

  8. Natural Selection in Action • Tibetan people in the Himalayas • Study on mice: example of genetic component related to behaviour http://fitgevitylifestyle.com/?paged=4

  9. Evolutionary change without selection: Genetic Drift • Change in genetic population due to chance. • Has greater impact in smaller populations http://smabiology.blogspot.com/2009_02_01_archive.html

  10. Evolutionary change without selection: Genetic bottlenecks • Genetic drift that results when there is a dramatic reduction in population.

  11. Genetic bottleneck (cont’d) Example of Bottleneck Effect: -By the end of the 19th century, hunting reduced the population of northern elephant seals to as few as 20 individuals.

  12. Genetic Drift (cont’d) -As a result of this population bottleneck, the genetic variation of the population was greatly reduced. -The population of northern elephant seals has since rebounded due to environmental protection, but it still has low genetic variation, leaving it susceptible to disease, etc.

  13. Evolutionary change without selection: Founder effect Founder Effect: Genetic drift that results when a small number of individuals separate from their original population and start a new population. -new population may have: -reduced genetic variation from the original population -a non-random sample of the genes in the original population

  14. The Founder effect Island The Mainland

  15. The Founder effect Population Island The Mainland

  16. The Founder effect A few individuals colonise a new isolated area The Mainland

  17. There may be a higher frequency of one allele in the founder population just by chance This allele needn’t have been very common in the original population

  18. The island population grows Island

  19. …after a few generations The green allele may be lost completely if individuals fail to leave offspring carrying it Island

  20. …after a few generations The green allele may be lost completely if individuals fail to leave offspring carrying it Island

  21. …after a few generations Mutations may occur creating new alleles Island

  22. …after a few generations The new allele becomes more common Island

  23. The 2 populations now look very different! Island The Mainland

  24. Founder effect (cont’d) • Polydactyly (extra fingers or sometimes toes) is commonly found in the Amish population in Eastern Pennsylvania due to the Founder Effect and a closed population.

  25. The Fugates • Small founding population • Mountain communities • 2 of the founders were carriers of a recessive allele • Blue skin!

  26. Skittles bottleneck game Different coloured skittles represent different alleles. • Count the number of individuals in the population in your bottle, calculate the frequency of each colour allele (%). • Mix your sample of alleles in the bottle. • Let 5 alleles through the bottleneck after a disaster causing a crash in population numbers. • Record the colours & numbers of these 5 alleles. • When each individual in this generation dies it can leave a maximum of 3 offspring (or 3 skittles of the same colour) unless you do not have enough of this particular colour, in which case the individual has failed to reproduce. Record the new allele frequencies. • Remove the original population from the bottle and put in the survivors. • Repeat the process of letting 5 individuals through a bottleneck, recording the allele frequencies, letting them reproduce if possible and recording the allele frequencies again. Repeat instructions 3-7 for 10 disasters

  27. Similarities and differences between the founder effect & bottlenecking

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