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Microevolution

Microevolution. BIO 1113/1114 Oklahoma City Community College. Dennis Anderson. Population. A population is all the members of a single species living in a defined geographical area at a given time. Gene Pool. All the alleles in a population.

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Microevolution

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  1. Microevolution BIO 1113/1114 Oklahoma City Community College Dennis Anderson

  2. Population • A population is all the members of a single species living in a defined geographical area at a given time.

  3. Gene Pool • All the alleles in a population. • The basis of evolution is a change in the frequency of alleles in a gene pool.

  4. Microevolution • A change of allele frequency within a population over a relatively short period of time.

  5. Five Agents of Microevolution • Five evolutionary forces can cause changes in allele frequencies within a population. • These agents of microevolution are: • mutation • gene flow • genetic drift • sexual selection • natural selection

  6. Mutations (a) (b) Normal Point mutation Normal Deletion correct nucleotide sequence incorrect nucleotide sequence complete chromosome 5 incomplete chromosome 5 Figure 17.3

  7. Mutations • Introduces new alleles into a population • Can cause a new characteristic • Most mutations are lethal • Mutation for no heart would be lethal • Some mutations are beneficial • Block infection of HIV

  8. Beneficial Mutation • Mutation for albinism was beneficial for bears who live on the ice and snow

  9. Gene Flow • When genes move from one population to another • Genes flow between the two populations below OKC Dallas

  10. Gene Flow

  11. Genetic Drift • Change in gene frequency when a small group of individuals leave or are separated from a larger population • Founder Effect • Bottleneck

  12. New Population 10% with A allele Founder Effect Original Population 1% has allele A 10 Founders • 10 people leave to found a new population • 1 of the founders has allele A • 10% of new population will have allele A

  13. Ellis-van Creveld Syndrome • Dwarfism • Extra fingers • Heart defects • High frequency in Amish population of Pennsylvania • A founder of the population had the allele for the syndrome

  14. Bottleneck • Most individuals in a population are wiped out • Only the alleles of the few survivors are passed on the next generation. • The result is that the survivors’ alleles are at a higher frequency in the descendants than the original population

  15. Bottleneck

  16. Sexual Selection • Females prefer to mate with males that display bright elaborate feathers. • More genes enter the gene pool from males with exotic colors.

  17. Natural Selection • Some individuals have traits that make it more likely that they will survive and pass on their genes than other individuals in a population.

  18. Natural Selection • Large talons are advantageous to eagles • Natural selection favors eagles with large talons • Nature selects for large talons in eagles

  19. Natural Selection &Tuberculosis • Number 1 killer in 1900 • Antibiotics decreased cases dramatically • 1980 very few cases • Bacteria that causes TB are constantly mutating • Mutant strains resistant to antibiotics are naturallyselectedto survive

  20. Evolution of Tuberculosis Cases of TB 1900 1980 2000

  21. Fitness • Having more offspring than do other members of the same population • More alleles of the fittest individuals will be passed on to the next generation

  22. Sickle Cell Anemia Frequency • Sickle cell anemia is most common in parts of Africa with malaria • Carriers who live in an environment with malaria have an advantage • Immune to malaria

  23. Why is the frequency of sickle cell anemia lower in African Americans than in native African populations from which they originated? • There is no selective advantage for the s allele in an environment with no malaria • The frequency of the s allele in the USA Black population has dropped significantly in the last 300 years.

  24. Selection Figure 17.13

  25. Stabilizing Selection • Average value selected for • Extreme values selected against

  26. Directional Selection • Favors values above or below average • Population will shift to the favored value

  27. Directional Selection Cranial capacity (the volume of the skull) has increased in hominins over time H. sapiens H. erectus H. ergaster 1400 H. habilis 1200 A. africanus 1000 A. afarensis 800 Cranial capacity (cubic centimeters) 600 400 200 4 3 2 1 Present Earliest fossil record (millions of years ago) Figure 17.12

  28. Disruptive Selection • Bothe extremes traits of a trait are favored • Birds with small bills and large bills are better feeders • In a specific enrironment

  29. The End

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