UNIT VIII EVOLUTION

1. UNIT VIII EVOLUTION • Big Campbell • Ch 22-28, 31 • Baby Campbell • Ch 13-17 • Hillis • Ch 15-18

2. I. EVOLUTION - WHAT IS IT? • “Descent with Modification” Earth’s many species are descendants of ancestral species that were diff. than present day species • Evolution – change in the genetic composition of a population over time. • “Change” – in the genetic composition (the alleles) • Population – group of organisms of one species in a certain habitat that interbreed to produce fertile offspring. November 24, 1859

3. II. Hardy-Weinberg Principle • Means used to determine if a population is evolving • Predicts allele frequency in a non-evolving population; that is, a population in equilibrium • States that allele frequencies in a population will remain constant from generation to generation if five conditions are met

4. II. Hardy-Weinberg Principle, cont • Five Conditions for Hardy-Weinberg Equilibrium: • No Mutations – gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated • Random Mating – if individuals mate preferentially within a population (inbreeding), random mixing of gametes does not occur and gene frequency changes. • No natural Selection – differences in the survival and reproductive success of individuals carry diff. genotypes and can alter allele frequencies. • Extremely large population size – the smaller the pop the more likely allele frequencies will fluctuate by chance from one generation to the next (genetic drift) • No gene flow (migration) – moving alleles into or out of populations can alter allele frequencies. If any of these conditions are not met, evolutionary change will occur!

5. II. Hardy-Weinberg Principle, cont • Hardy-Weinberg Equation • p = frequency of one allele (A) • q = frequency of other allele (a) • p + q = 1 (sum of 2 alleles = 1 or 100%) • Therefore, • p = 1 - q • q = 1 - p • Genotype Frequency • AA = p2 • aa = q2 • Aa = 2pq • To determine distribution of genotype frequencies in a population → • p2 + 2pq + q2 = 1

6. Ex: PKU in the US • Autosomal Recessive • Occurs 1 in 10,000 births • q2 = .0001 • q = .01 • p = 1 - .01 = .99 • What % of individuals are carriers for PKU? • 2pq = 2(.99)(.01) = .0198 or 2%

7. II. Hardy-Weinberg Principle, cont Hardy-Weinberg Practice Problems • If you know that you have 16% recessive fish (bb), . . . • q 2 = • q = • Therefore, p = • To calculate the frequency of each genotype … • p2 = • 2pq = • What is the expected percentage of heterozygous fish?

8. II. Hardy-Weinberg Principle, cont • Hardy-Weinberg Practice Problems, cont • If in a population of 1,000, 90 show recessive phenotype (aa), use Hardy-Weinberg to determine frequency of allele combinations. • In people light eyes are recessive to dark. In a population of 100 people, 36 have light eyes. What percentage of the population would be … • Homozygous recessive? • Homozygous dominant? • Heterozygous?

9. II. Hardy-Weinberg Principle, cont • The ability to roll the tongue is a dominant trait. … 75% of the students at Kingwood Park High School have the ability to roll the tongue. Assuming the student population is 1700, • How many students would exhibit each of the possible genotypes? • How many students would exhibit each of the possible phenotypes?

10. III. A HISTORY OF EVOLUTIONARY THEORY • Aristotle (384-322 BCE) • Scala Naturae • Carolus Linnaeus (1707-1778) • Taxonomy

11. III. A HISTORY OF EVOLUTIONARY THEORY, cont

12. III. A HISTORY OF EVOLUTIONARY THEORY, cont • Charles Darwin (1809-1882)

13. III. A HISTORY OF EVOLUTIONARY THEORY, cont • Darwin, cont • Observed many examples of adaptations • Inherited characteristics that enhance organisms’ survival and reproduction • Based on principles of natural selection • Populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others • Differential reproductive success

14. III. A HISTORY OF EVOLUTIONARY THEORY, cont • Darwin’s Conclusions • Based on his own observations and the work of other scientists, Darwin realized … • Members of a population often vary greatly in their traits. • Traits are inherited from parents to offspring. • All species are capable of producing more offspring that their environment can support, therefore …

15. III. A HISTORY OF EVOLUTIONARY THEORY, cont • Darwin concluded … • Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals. • This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations. • Descent with Modification

16. III. A HISTORY OF EVOLUTIONARY THEORY, cont • Artificial Selection

17. III. A HISTORY OF EVOLUTIONARY THEORY, cont • Post-Darwin • Neo-Darwinism/Modern Synthesis Theory • Epigenetics

18. IV. EVIDENCE FOR EVOLUTION • Direct Observation • Antibiotic/Drug Resistance

19. IV. EVIDENCE FOR EVOLUTION, cont • Fossil Record • Succession of forms over time • Transitional Links • Vertebrate descent

20. IV. EVIDENCE FOR EVOLUTION, cont • Homology • Homologous structures • Vestigial organs • Snakes • Cetaceans • Flightless birds

21. IV. EVIDENCE FOR EVOLUTION, cont • Convergent Evolution • Independent evolution of similar features in different lineages • Analogous structures

22. IV. EVIDENCE FOR EVOLUTION, cont • Biogeography • Geographical distribution of species • Continental Drift • Pangaea • Endemic species • Islands are inhabited by organisms most closely resembling nearest land mass

23. IV. EVIDENCE FOR EVOLUTION, cont • Comparative Embryology • Pharyngeal Pouches • Gill slits • Tail

24. IV. EVIDENCE FOR EVOLUTION, cont • Molecular Biology • Similarities in DNA, proteins, genes, and gene products • Common genetic code

25. V. MICROEVOLUTION • A change in the gene pool of a population over a succession of generations • Five main causes: • Mutation • Non-Random Mating • Natural Selection • Genetic Drift • Gene Flow

26. V. MICROEVOLUTION, cont • Genetic Drift • Changes in the gene pool due to chance. • More often seen in small population sizes. • Usually reduces genetic variability. • There are two situations that can drastically reduce population size: • Bottleneck Effect • Founder Effect

27. Bottleneck Effect Type of genetic drift resulting from a reduction in population (natural disaster) Surviving population is no longer genetically representative of the original population Founder Effect Due to colonization by a limited number of individuals from a parent population Gene pool is different than source population V. MICROEVOLUTION, cont

28. V. MICROEVOLUTION, cont • Gene Flow • Genetic exchange due to the migration of fertile individuals or gametes between populations – tends to reduce differences between populations

29. V. MICROEVOLUTION, cont • Mutations • A change in an organism’s DNA (gametes; many generations); original source of genetic variation (raw material for natural selection)

30. V. MICROEVOLUTION, cont • Nonrandom Mating • Inbreeding – reduces fitness by putting an individual at a greater risk of harmful recessive traits. • Assortative mating – individuals with similar genotypes/phenotypes mate more frequently than expected

31. V. MICROEVOLUTION, cont • Natural Selection • Blend of Chance and Sorting chance in the creation of new genetic variations; sorting b/c natural selection favors some alleles over others • Relative fitness – contribution an individual makes to the gene pool of the next generation • Only form of microevolution that adapts a population to its environment

32. VI. VARIATION IN POPULATIONS • Genetic Variation is the “substrate” for evolution • Maintained through … • Polymorphism • Coexistence of 2 or more distinct forms of individuals (morphs) within the same population • Geographical Variation • Differences in genetic structure between populations (cline)

33. VI. VARIATION, cont • Mutation and Recombination • Diploidy • 2nd set of chromosomes hides variation in the heterozygote • Balanced Polymorphism • Heterozygote Advantage • Frequency-Dependent Selection • Survival & reproduction of any 1 morph declines if it becomes too common • Parasite/host

34. VII. A CLOSER LOOK AT NATURAL SELECTION • Natural Selection • Not a random process → Dynamic process • Increases frequency of alleles that provide reproductive advantage • Fitness

35. VII. CLOSER LOOK AT NATURAL SELECTION, cont • Natural selection is the only evolutionary mechanism for adaptive evolution

36. VII. CLOSER LOOK AT NATURAL SELECTION, cont • Three ways in which natural selection alters variation • Directional • Disruptive • Stabilizing

37. VII. CLOSER LOOK AT NATURAL SELECTION, cont • Sexual Selection • Can result in sexual dimorphism - secondary sex characteristic distinction • Intrasexual Selection - within the same sex; individuals of one sex compete directly for mates of the opposite sex • Intersexual Selection - individuals of one sex are choosy in selecting their mate (male showiness)

38. VIII. MACROEVOLUTION • Macroevolution • Refers to the formation of new taxonomic groups • Due to an accumulation of microevolutionary changes • AKA Speciation • “Species” • Morphological Species Concept - charac. species by body shape & other features; can be applied to sexual & asexual organisms • Ecological Species Concept – views a species in terms of its niche; which is the sum of how members interact w/living & non-living parts of environ; can accommodate sex & asexual • Phylogenetic Species Concept – smallest group of individuals that share a common ancestor; forming 1 branch on tree of life

39. VIII. MACROEVOLUTION, cont • Biological Species Concept • Described by Ernst Mayr in 1942 • A population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring; in other words, similar organisms that can make babies that can make babies  • Can be difficult to apply to certain organisms . . .

40. VIII. MACROEVOLUTION, cont • Reproductive Isolation • Prevent closely related species from interbreeding when their ranges overlap. • Divided into 2 types • Prezygotic • Postzygotic

41. VIII. MACROEVOLUTION, cont Prezygotic Reproductive Barriers

42. VIII. MACROEVOLUTION, cont Postzygotic Reproductive Barriers

43. VIII. MACROEVOLUTION, cont • Speciation • Fossil record shows evidence of bursts of many new species, followed by periods of little chance • Known as punctuated equilibrium • Other species appear to change more gradually • Gradualism fits model of evolution proposed by Darwin

44. VIII. MACROEVOLUTION, cont • Modes of Speciation • Based on how gene flow is interrupted • Allopatric • Populations segregated by a geographical barrier; can result in adaptive radiation (island species) • Sympatric • Reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes

45. IX. HISTORY OF LIFE ON EARTH

46. IX. HISTORY OF LIFE ON EARTH, cont • Formation of Organic Molecules • Oparin/Haldane Hypothesis • Primitive Earth’s atmosphere was a reducing environment • No O2 • Early oceans were an organic “soup” • Lightning & UV radiation provided energy for complex organic molecule formation • Miller/Urey Experiment • Tested Oparin/Haldane hypothesis • Simulated atmosphere composed of water, hydrogen, methane, ammonia • All 20 amino acids, nitrogen bases, ATP formed • Hypothesis was supported

47. IX. HISTORY OF LIFE ON EARTH, cont

48. IX. HISTORY OF LIFE ON EARTH, cont

50. IX. HISTORY OF LIFE ON EARTH, cont • Mass Extinctions