1. Chapter 16 Evolution of Populations

2. 16-1: Genes and Variation natural selection relies on variation genes are the source of inheritable variation when variation occurs, nature selects the successful ones individuals do not change, a population does

3. Genes and Variation At least two different alleles account for inherited traits. –Body size, coat color, seed shape “Invisible” variation also present –Small differences in biochemical processes

4. Genes and Variation Individual organisms are heterozygous for many genes 15% of genes in insects 4 – 8% in fish, reptiles, and mammals

5. Evolution as Genetic Change evolutionary biologists study populations –collection of individuals of the same species in a given area –share a gene pool relative frequency: number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur What is the relative frequency of the purple allele?

6. Genetic Variation within a Species species: group of similar organisms that breed with each other and produce viable offspring because they share the same gene pool How do mutations occur? –Mistakes in replication, radiation, and chemicals Gene Shuffling - Meiosis

7. Genetic Variation within a Species How many different combinations of genes can be produced from homologous x- somes in a human? –8.4 million Number of phenotypes produced for a trait depends on how many genes control the trait –Single-gene trait –Polygenic trait

8. Single-gene and Polygenic

9. QUESTION of the DAY Mar 17 The success of an organism in surviving and reproducing is a measure of A. an adaptation to an environmental factor B. its fitness C. its polygenic traits D. single gene traits

10. 16-2 Evolution as Genetic Change Why does natural selection never act on specific genes? An entire organism either survives and reproduces or dies out. Organisms that die do not contribute to gene pool. Relative frequencies within a population change over time.

11. Natural Selection on Single Gene Traits Leads to changes in allele frequencies Consider a population of lizards… Normal skin = Brown Mutations produce Red and Black skin Predict the number of red lizards after 30 generations if the environment the lizards live in is a desert. Black lizards?WHY?

12. Natural Selection on Polygenic Traits What type of curve is produced when measuring a range of phenotypes? Bell curve Interpret the phenotypes found within the individuals of this population.

13. Three types of Selection Directional Selection – individuals at one end of the curve have higher fitness than those in middle or at the end. Dotted line = Original distribution of individuals

14. Types of Selection Stabilizing Selection – Individuals near the center of the curve have higher fitness than any other individuals. Dotted line = Original distribution of human babies

15. Types of Selection Disruptive Selection – Individuals at upper and lower ends of curve have higher fitness than those in the middle. Dotted line = Original distribution of individuals

16. Types of Adaptations Morphological Adaptation: Structural feature that aids a species in fitting into its environment. Physiological Adaptation: An adjustment of the body involving metabolic processes that allows an organism to best adapt to its environment. Behavioral Adaptation: Traits that develop to better allow an organism to survive or reproduce. –Bears hibernating in winter –Sheep running away from types of noises

17. Examples

18. QUESTION of the DAY Mar 18 When average sized seeds become more scarce but smaller and larger seeds are still available as food sources, the type of selection that represents this change is A. Directional B. Disruptive C. Stabilizing D. Drifting

19. GENETIC DRIFT What controls genetics and the passing down of genes? PROBABILITY Genetic drift: random change in the frequency of a gene that happens by chance –Greater # of changes as population sizes decrease Founder effect – change in allele frequencies due to the migration of a small subgroup of individuals.

20. Hardy-Weinberg Principle states that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change only applies during genetic equilibrium: when allele frequencies remain constant Conditions to maintain equilibrium random mating very large population no movement into or out of the population no mutations no natural selection

21. Calculating Gene Frequencies when a population is in Hardy-Weinberg equilibrium, genotypes can be calculated from allele frequencies p + q = 1 p 2 + 2pq + q 2 = 1 p = dominant allele q = recessive allele p 2 = homozygous dominant 2pq = heterozygous q 2 = homozygous recessive

22. Hardy-Weinberg Problems In a population of 3000 fruit flies, 270 flies have white eyes. White eye color is the recessive trait. Determine the frequencies of the red and white eye color alleles. How many flies are heterozygous for red eye color? APPLY the 2 H-W Equations.

23. SOLUTION STEP 1 – Determine q 2 STEP 2 – Find q and p STEP 3 – Determine p 2 STEP 4 – Find 2pq STEP 5 – Find # of heterozygous flies

24. Hardy-Weinberg Problem Coloration in the scarlet tiger moth is listed below for 1612 individuals. White-spotted (AA) = 1469 Intermediate (Aa) = 138 Little spotting (aa) =5 Calculate the following frequencies. A, a, AA, Aa, and aa

25. Question of the DAY March 19 When a population is in Hardy-Weinberg equilibrium, which of the following is true. A. Individuals interbreed with other populations B. Genetic mutations can occur in recessive alleles. C. Allele frequencies are true over long periods of time. D. Random mating can occur within a single population.

26. 16-3: The Development of New Species speciation: process in which new species evolve from old ones niche: combination of an organism’s profession and the place it lives no two species can occupy the same niche in the same location for a long period of time any species that occupies an unoccupied niche will better survive and potentially form a new species

27. Process of Speciation new species form when populations are separated reproductive isolation: when populations are separated so they do not interbreed gene pools become dissimilar in different environments Darwin’s finches

28. Mechanisms of Reproductive Isolation Behavioral isolation – two populations –Capable of interbreeding –Differences in courtship rituals or reproductive strategies –Eastern and western meadowlarks Different mating songs

29. Mechanisms Geographic isolation – two population separated by geographic barriers –Mountains, rivers, bodies of water –May not isolate every organism from one another

30. Mechanisms Temporal isolation – two or more species reproduce at different times. Similar orchids living in a rain forest. –Each releases pollen at a different time

31. Peter and Rosemary Grant Documented effects in finches on Galapagos Individual birds with different beak sizes had different chances of survival during a drought Big-beaked birds –obtain food when scarce –mate with other big-beaked birds

32. Speciation in Darwin’s Finches 1. Founders species – first finches arrive on Galapagos 2. Geographic isolation - Some finches arrived on another island 3. Different Gene Pools on each island 4. Reproductive isolation – Two species on same island 5. Competition – both species compete on same island 6. Continued evolution – produced 13 different species

33. Speciation and Adaptive Radiation adaptive radiation: one species produces many species –also known as divergent evolution convergent evolution: different species evolve to have similar appearances and behaviors analogous structures: structures similar in appearance and function but have different origins

34. Pace of Evolution punctuated equilibrium: involves long periods of stability that are interrupted by episodes of rapid change gradualism: evolution occurs slow and steady over a long period of time