1 / 19

Evolution of Populations Chapter 23.3-23.4

Evolution of Populations Chapter 23.3-23.4. AP Biology. Recap. 23.1-23.2. Two Types of Evolution. Macroevolution. Microevolution. Change that occurs within a species Change in gene frequencies Focus of Darwin’s theory of evolution via natural selection.

zuwena
Download Presentation

Evolution of Populations Chapter 23.3-23.4

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Evolution of PopulationsChapter 23.3-23.4 AP Biology

  2. Recap 23.1-23.2

  3. Two Types of Evolution Macroevolution Microevolution Change that occurs within a species Change in gene frequencies Focus of Darwin’s theory of evolution via natural selection • Evolution that takes place over LONG periods of time • Change on a grand scale • Mass extinctions

  4. How can we study microevolution? • Study population genetics to understand changes that occur within a species • Hardy-Weinberg

  5. There are 3 mechanisms for evolution • Natural Selection • Leads to an accumulation of favorable adaptations in a population • Genetic Drift • Chance events that alter allele frequencies • Gene Flow • The transfer of alleles between populations

  6. Natural selection, genetic drift, and gene flow can alter allele frequencies in a population 23.3

  7. Review: Natural Selection • This is a change in gene frequencies due to differential reproductive success. • Example: antibiotic resistance • Variation already present • Introduction of antibiotic selects for those with higher resistance • Frequencies for the resistance gene increase over time

  8. Genetic Drift • Changes in the gene pool of a small population due to chance (random) • Founder Effect or Bottleneck Effect

  9. Genetic Drift: Founder Effect • A few (random) individuals from a population start a new population with a different allele frequency than the original population

  10. Genetic Drift: Bottleneck Effect • The population experiences a huge decrease in size • Result: severe reduction in diversity of the original gene pool because a small percentage of chance survivors remain • Endangered species can experience this

  11. BB BB BB BB BB bb Gene Flow • Migration of fertile individuals, or the transfer of gametes, between populations • Populations may gain or lose alleles • Reduces differences between neighboring populations

  12. Natural selection is the only mechanism that consistently causes adaptive radiation 23.4

  13. Natural Selection • Natural selection results in development of features which increase an organism’s likelihood for survival and reproduction—adaptations • Therefore, Darwin’s explanation of evolution goes like this: • Adaptation + natural selection  change within species • Leads to adaptive evolution

  14. Modes of Natural Selection • Directional Selection – favors variants of one extreme • Disruptive Selection – Opposite phenotypic extremes favored over intermediate • Stabilizing Selection – favors intermediate variants by selecting against extreme phenotypes

  15. Maintaining Variation • Natural selection is the main mechanism of evolution • For this to work, variation must be maintained • Variation is good (why?)

  16. Conserving Variation: Polymorphism • The presence of two or more distinct phenotypes in a population • Example: sexual dimorphism • Leads to the enigma of sexual reproduction • Evolutionary advantage outweighs cost of sex • Costs: energy, resources, competition • Advantage: pass on genes, variation of genes (2 parents vs. 1 parent, meiosis)

  17. Conserving Variation: Diploidy • The presence of homologous chromosomes (one from mom, one from dad) maintains variety in the population • A dominant allele can cover up a harmful recessive one • Example: cystic fibrosis

  18. Conserving Variation: Heterozygote Advantage • Heterozygotes more likely to survive than homozygotes • Example: sickle-cell anemia and malaria resistance

  19. Natural Selection isn’t perfect • Nature can only select for what traits are present. • Ancestry is a legacy that is modified; nothing is built from scratch. • Adaptations are often compromises. • Chance, natural selection and the environment interact.

More Related