EVOLUTION/POPULATION GENETICS

1. EVOLUTION/POPULATION GENETICS CH. 15-16

2. SOME INFLUENCES ON DARWIN’S THOUGHT • James Hutton • Charles Lyell • Jean-Baptiste Lamarck • Thomas Malthus • Alfred Russell Wallace

3. Contributor’s to Darwin’s thinking included: : • Charles Lyell –uniformatarianism • Georges Cuvier – species extinction (Catastrophism) • Thomas Malthus – struggle for existence (resources)

4. Contributor’s to Darwin’s thinking included: : • James Hutton - Gradualism • Jean Baptiste Lamarck – Inheritance of acquired Characteristics and Law of Use and Disuse • Alfred Russell Wallace – organisms evolved from common ancestors

5. Hutton’s Theory of Geological Change • James Hutton, 1795, Scottish geologist • Studied invertebrate fossils in Paris Museum • Described The Geological Forces That Have Changed Lifeon Earth Over Millions of Years (erosion, earthquakes, volcanoes…)

6. Hutton’s Theory of Geological Change • Changes in Earth’s crust is due to slow continuous processes • Idea Known as Gradualism

7. Charles Lyell (1797-1875) • Proposed theory of Uniformitarianism • Geological processes occur at uniform rates building & wearing down Earth’s crust • Proposed that the Earth was millions of years instead of a few thousand years old

8. Principles of Geology • Published by Lyell Just Before The Beagle Set Sail & read by Darwin • Explained Geological Processes That Shaped The Earth • Helped Darwin Understand Sea Shells In The Andes Mountains At 12,000+ Feet • Expanded Earth’s Age

9. Lamarck’s Theory of Evolution • Jean-Baptiste Lamarck, 1809 • One Of First Scientists To Understand That Change Occurs Over Time • Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime • Said acquired changes were passed to offspring

10. Lamarck’s Theory of Evolution • Idea called Law of Use and Disuse • If a body part were used, it got stronger • If body part NOT used, it deteriorated

11. Lamarck’s Theory of Evolution • Inheritance Of Acquired Traits • Traits Acquired During One’s Lifetime Would Be Passed To Offspring Clipped ears of dogs could be passed to offspring!

12. Lamarck’s Mistakes • Lamarck Did NOT Know how traits were inherited (Traits are passed through genes) • Genes Are NOT Changed By Activities In Life • Change Through Mutation Occurs Before An Organism Is Born

13. Population Growth • Thomas Malthus, 1798 • Economist • Observed Babies Being Born Faster Than People Were Dying • Population size limited by resources such as the Food Supply

14. The Struggle for Existence • Malthus’ Influence: • High Birth Rates & Limited Resources Would Force Life & Death Competition • Each Species Struggles For: • Food • Living Space • Mates

15. Population Growth • Malthus Reasoned That If The Human Population Continued To Grow Unchecked, Sooner or Later There Would Be Insufficient Living Space & Food For Everyone • Death Rate Will Increase To Balance Population size & Food Supply

16. Population Growth • Darwin Realized Malthus’s Principles Were Visible In Nature • Plants & Animals Produce Far More Offspring Than Can Be Supported • Most Die • If They Didn’t – Earth Would Be Overrun

17. Wallace’s Contribution • Alfred Russell Wallace Independently came to same Conclusion as Darwin that species changed over time because of their struggle for existence • When Darwin read Wallace’s essay, he knew he had to publish his findings

18. Darwin's Theory • Individual Organisms In Nature Differ From One Another. Some Of This Variation Is Inherited 2. Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do not Reproduce

19. Darwin's Theory • Because More Organisms Are Produced Than Can Survive, Members Of Each Species Must Compete For Limited Resources • Because Each Organism Is Unique, Each Has Different Advantages & Disadvantages In The Struggle For Existence

20. Darwin's Theory • Individuals Best Suited To Their Environment Survive & Reproduce Successfully – Passing Their Traits To Their Offspring. • Species Change Over Time. Over Long Periods, Natural Selection Causes Changes That May Eventually Lead To New Species

21. Darwin's Theory • Species Alive Today Have Descended With Modifications From Species That Lived In The Past • All Organisms On Earth Are United Into A Single Tree Of Life By Common Descent

22. The fossil record Geographic distribution of living species Homologous body structures Similaritiesin early development Physical remains of organisms Common ancestral species Similar genes Similar genes Concept Map Section 15-3 Evidence of Evolution includes which is composed of which indicates which implies which implies

23. Fossil Record • Old remains of the past • Earth is Billions of Years Old • Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time

24. Homologous Structures

25. Geographic Distribution of Living Species Section 15-3 Beaver Beaver Muskrat Beaver andMuskrat Coypu Capybara Coypu andCapybara NORTH AMERICA Muskrat Capybara SOUTH AMERICA Coypu

26. HOMOLOGOUS STRUCTURES Section 15-3 Turtle Alligator Bird Mammal Ancient lobe-finned fish

27. In evolutionary biology, homology refers to any similarity between characteristics of organisms that is due to their shared ancestry. The word homologous derives from the ancient Greek ομολογειν, 'to agree'.

28. Evidence for Evolution - Comparative Embryology Similarities In Embryonic Development

29. Homologous Body Structures • Not All Serve Important Functions • Vestigial Organs- no longer serve a function • Appendix In Man • Legs On Skinks

30. Similarities in DNA Sequence

31. Evolutionary Time Scales Macroevolution:Long time scale events that create and destroy species.

32. Evolutionary Time Scales Microevolution: Short time scale events (generation-to-generation) that change the genotypes and phenotypes of populations

33. VARIATION & GENE POOLS Section 16-1 Sample Population Frequency of Alleles allele for brown fur allele for black fur 48% heterozygous black 16% homozygous black 36% homozygous brown Gene pool Relative frequency # of times an allele occurs in a gene pool, compared w/ the # of times other alleles for the same gene occur

34. MUTATION • THE ULTIMATE SOURCE OF GENETIC VARIATION!!!!!!

35. Phenotypes for Single-Gene Trait- # of phenotypes a given trait has is determined by how many genes control the trait Section 16-1 * Controlled by a single gene that has 2 alleles leads to 2 distinct phenotypes 100 80 60 40 20 0 Frequency of Phenotype (%) Widow’s peak No widow’s peak Phenotype

36. Generic Bell Curve for Polygenic Trait: many possible genotypes and phenotypes Section 16-1 *Controlled by 2/ more genes (2/ more alleles) Frequency of Phenotype Phenotype (height)

37. NATURAL SELECTION ON POLYGENIC TRAITS: 3 MODELS Section 16-2 Key Directional Selection Low mortality, high fitness High mortality, low fitness Food becomes scarce. Favors traits at 1 extreme of a range of traits

38. Graph of Stabilizing Selection Section 16-2 Stabilizing Selection Individuals with the most common trait are most adapted, while individuals who differ from the norm are poorly adapted. Key Low mortality, high fitness High mortality, low fitness Selection against both extremes keep curve narrow and in same place. Percentage of Population Birth Weight

39. Stabilizing Selection Natural selection acts in opposite directions *** “Heterozygote Advantage”- ind who is heterozygous for a particular gene has a greater fitness than a homozygous ind EX: Distribution of sickle-cell allele coincides with the occurrence of malaria SS Normal hemoglobin ss Sicke-cell disease Ss- codominance (protects against malaria)

40. Graph of Disruptive Selection Section 16-2 Disruptive Selection Largest and smallest seeds become more common. Key Population splits into two subgroups specializing in different seeds. Low mortality, high fitness Number of Birdsin Population Number of Birdsin Population High mortality, low fitness Beak Size Beak Size When both extreme phenotypes are favored by natural selection Acts in opposite directions

41. GENTIC DRIFTA RANDOM CHANGE IN ALLELE FREQUENCY • IN SMALL POPULATIONS, INDIVIDUALS THAT CARRY A PARTICULAR ALLELE MAY LEAVE MORE DESCENDANTS THAN OTHER INDIVIDUALS, JUST BY CHANCE. • OVER TIME, A SERIES OF CHANCE OCCURRENCES OF THIS TYPE CAN CAUSE AN ALLELE TO BECOME COMMON IN A POPULATION. • FOUNDER EFFECT: A SITUATION IN WHICH ALLELE FREQUENCIES CHANGE AS A RESULT OF THE MIGRATION OF A SMALL SUBGROUP OF A POPULATION.

42. Genetic Drift Section 16-2 Sample of Original Population In small populations, an allele can become more or less common by chance (explain how allele frequencies can fluctuate unpredictably from 1 gen to the next) Descendants Founding Population A Founding Population B

43. Genetic Drift Section 16-2 Sample of Original Population Descendants FOUNDER EFFECT: 2 small groups from a large, diverse population could produce new populations that differ from the original population Founding Population A Founding Population B

44. Genetic Drift Section 16-2 Sample of Original Population Descendants Founding Population A Founding Population B

45. EVOLUTION VERSUS GENETIC EQUILIBRIUM HARDY-WEINBERG PRINCIPLE: ALLELE FREQUENCIES IN A POPULATION WILL REMAIN CONSTANT AS LONG AS FIVE CONDITIONS (FACTORS) REMAIN CONSTANT. GENETIC EQUILIBRIUM IS REACHED. (IS THE POPULATION EVOLVING?)

46. 5 CONDITIONS REQUIRED TO MAINTAIN GENETIC EQUIIBRIUM • RANDOM MATING - Select mates w/o bias 2. LARGE POPULATION - Genetic drift does not affect large pops 3. NO MOVEMENT INTO OR OUT OF THE POPULATION - no intro of new allele 4. NO MUTATION - no new allele introduced • NO NATURAL SELECTION - No phenotype can have selective advantage DOES THIS EVER HAPPEN?????

47. In 1908, Hardy and Weinberg independently demonstrated that DOMINANT ALLELES DO NOT REPLACE RECESSIVE ALLELES IN A POPULATION!

48. HARDY-WEINBERG EQUATION You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: The frequency of the "aa" genotype. The frequency of the "a" allele. The frequency of the "A" allele. The frequencies of the genotypes "AA" and "Aa." The frequencies of the two possible phenotypes if "A" is completely dominant over "a."

49. FREQUENCY OF aa GENOTYPE: 36% (GIVEN) • FREQUENCY OF a ALLELE:The frequency of aa is 36%, which means that q2 = 0.36, by definition. If q2 = 0.36, then q = 0.6, again by definition. Since q equals the frequency of the a allele, then the frequency is 60%. • The frequency of the "A" allele. Answer: Since q = 0.6, and p + q = 1, then p = 0.4; the frequency of A is by definition equal to p, so the answer is 40%.

50. The frequencies of the genotypes "AA" and "Aa." Answer: The frequency of AA is equal to p2, and the frequency of Aa is equal to 2pq. So, using the information above, the frequency of AA is 16% (i.e. p2 is 0.4 x 0.4 = 0.16) and Aa is 48% (2pq = 2 x 0.4 x 0.6 = 0.48). • The frequencies of the two possible phenotypes if "A" is completely dominant over "a." Answers: Because "A" is totally dominate over "a", the dominant phenotype will show if either the homozygous "AA" or heterozygous "Aa" genotypes occur. The recessive phenotype is controlled by the homozygous aa genotype. Therefore, the frequency of the dominant phenotype equals the sum of the frequencies of AA and Aa, and the recessive phenotype is simply the frequency of aa. Therefore, the dominant frequency is 64% and, in the first part of this question above, you have already shown that the recessive frequency is 36%.