Evolution of Populations

1. Evolution of Populations Objectives: 12.1 Identifying ways in which the theory of evolution explains the nature and diversity of organisms 12.2 Describing natural selection, survival of the fittest, geographic isolation, and fossil record AOD B.12.4 Describe evidence of species variation due to climate, changing

2. Section 1: Genes and Variation • Review: • Mendel: • Pea plants • Punnett squares • Crosses between 2 heterozygous parents predict: • Phenotype ration of 3:1 • Genotype ratio of 1:2:1 • Lamark • Darwin: • Made observations of species (living and fossils) while on the HMS Beagle. • Could NOT: • explain how traits were passed from one generation to another. • How new species appeared and others became extinct.

3. Section 1: Genes and Variation • Sources of Variation: • Mutations --- changes in nucleotide bases • Gene shuffling --- • Due to independent assortment of chromosomes during meiosis • 23 pairs of chromosomes (humans) can yield 8.4 million different combinations of genes! Then add in crossing over!!!! • Kind of like a deck of 52 playing cards --- your chance of drawing an ace at any time is 4/52, or 1/13, no matter how many times you shuffle the deck.

4. Section 1: Genes and Variation • Gene Pools • Single-gene activity • Single-gene trait vs. polygenic trait • Polygenic will yield many more possible combinations • Variation and Gene Pools • Gene pool: all the genes, and their different alleles, present in a population • Relative frequency: the number of times an allele occurs in a gene pool, compared to the total numbers of alleles present; expressed as a percentage. • Use our class gene pool data as an example. • Again, how would an introduction of non-tongue-rollers affect our population?

5. Section 2: Evolution as Genetic Change • Review: What is evolutionary “fitness”? • Answer: the ability of an organism to pass on its traits/genes to its offspring • So an evolutionary adaptation is any genetic change that increases an individual’s chances of passing on its genes. • Evolution is any change over time in the relative frequencies of alleles in a population. (Refer to our gene pool activity?)

6. Section 2: Evolution as Genetic Change • Natural Selection on Single-Gene Traits: • Can lead to changes in allele frequencies in a population, which is what we call _______________ . • In your camouflage experiment, did you have any alleles (colored beads) disappear from your population? • Why? • What did this do to the gene pool for “bead color”? • What was the cause of this change? • Lizard color mutation example on pp.397-398 of textbook (next slide)

7. What are some Possible reasons the red mutation did not survive, but the black mutation survived and thrived?

8. Section 2: Evolution as Genetic Change • Natural Selection on Polygenic Traits: • Normal distribution of polygenic traits resembles a bell curve: Source: http://sixminutes.dlugan.com/good-public-speaker-average/

9. Section 2: Evolution as Genetic Change • Natural selection can affect the distribution of polygenic phenotypes in three ways: • Directional selection – shifts toward one end or the other • Stabilizing selection – favors individuals in the middle of the graph, putting more individuals there, and making the distribution curve more narrow • Disruptive selection – • conditions favor extremes at end of bell curve, so curve will dip in the center • Can result in two separate curves

10. Source: http://cosbiology.pbworks.com/w/page/24299272/13-02%20%E2%80%93%20Evolution%20as%20Genetic%20Change

11. Section 2: Evolution as Genetic Change • Genetic Drift: • In small populations, results may not be those predicted by a Punnett square (think of purposeful breeding of species, or populations without an influx of “outsiders”). • An allele can become more or less common simply by chance, if an allele is passed on more frequently than another. • The random change in allele frequency is called genetic drift. • Occurs commonly when a small population “settles” a new habitat --- called founder effect. • Which type(s) of selection would a graph of the phenotype(s) resemble?

12. Section 2: Evolution as Genetic Change • Evolution vs. Genetic Equilibrium: • Hardy-Weinberg principle: allele frequency will remain constant unless one or more factors cause it to change. • Five conditions required to maintain genetic equilibrium: • Random mating • Very large population • No movement into or out of the population • No mutations • No natural selection • What are the chances of these conditions ALL being met??

13. Section 2: Evolution as Genetic Change • Mutiny on the Bounty and Pitcairn Island in the South Pacific • How would each of these conditions affect allele frequency, if not met? • Give an example of how each of these conditions could be met.

14. Section 16-3The Process of Speciation • Speciation: the formation of a new species • What is the definition of a species? • For a new species to form, enough genetic change must occur so that the “new” species can no longer effectively reproduce with the “old” species. • This is termed reproductive isolation, and the two species now have separate gene pools.

15. Section 16-3The Process of Speciation • Reproductive isolation can take several forms: • Behavioral isolation --- the species are capable of interbreeding, but do not respond to each other’s overtures (different mating rituals or reproductive strategies). • Geographic isolation --- may or may not lead to separate species; natural selection does work separately on each group. • Temporal isolation --- different mating times (EX: pollen production)

16. Darwin’s Finches & the Grant’s Source: http://myweb.rollins.edu/jsiry/Grants'finch-study.html

17. Section 16-3The Process of Speciation • How speciation worked in the finches: • Founder effect: A few finches flew from the South American mainland to one of the Galapagos Islands --- probably blown there in a storm. • Geographic isolation: At some point, some of these birds flew to another of the islands. The two populations were separated by open water, creating two separate gene pools.

18. Section 16-3The Process of Speciation • How speciation worked in the finches: • Changes in gene pool: As birds better suited to the environment on each island survived better, natural selection resulted in directional selection --- especially for beaks. • Reproductive isolation: Finches are choosy about partners and inspect beaks closely. Once the beaks were different, they would not mate with each other ---- EVEN THOUGH THEY PROBABLY COULD! (Separate gene pools = separate species)

19. Section 16-3The Process of Speciation • How speciation worked in the finches: • Ecological competition: When the two species live on the same island, they compete for food. (survival of the fittest) • Continued evolution: As the pattern repeated itself many times, 13 different species (or more) have evolved, each specialized to survive in different niches.

20. Section 16-3The Process of Speciation • Why do we care? • Discussion of antibiotic-resistant bacterial strains and pesticide-resistant pests. (Optional reading: Issues in Biology, p.403)