1. Chapter 17 Population Genetics

2. Genes & Variation What were the two big gaps in Darwin’s theory? 1.He had no idea how heritable traits were passed on to the next generation. 2.He had no idea how the variation within a population appeared. The connection between Mendel & Darwin wasn’t made until the 1930s. Charles Darwin

3. Genes & Variation Key Ideas: 1. Natural selection acts on phenotypes, not genotypes. - Natural selection acts on the whole organism, not a single a gene. 2. A single gene pair could affect the phenotype to the point that the organism is no longer fit.

4. Genes & Variation What is a population? A group of individuals of the same species that live in the same area & interbreed. What is a gene pool? All of the genes (alleles) in a population. Population of wild pigs Gene Pool

5. Genes & Variation What is relative frequency (allele frequency)? 1.The number of times an allele occurs in the gene pool 2.Often expressed as a percentage or a decimal. 3.Example: 100 alleles in the pool. 75 dominant alleles has a frequency of.75 (75/100). Allele frequency has nothing to do with whether the allele is dominant or recessive.

6. Genes & Variation What is evolution in genetic terms? Any change in the relative frequencies of alleles within a population over time.

7. Genes & Variation What are the sources of genetic/heritable variation? 1.Mutation – any change in DNA base sequence. Mutations within the germ line (eggs & sperm) are the ones that can be passed on to the next generation. 2.Genetic Recombination – This is the gene shuffling that occurs during meiosis. - independent assortment - crossing-over - some alleles from Dad & some from Mom 3.Lateral Gene Transfer – Transformation in bacteria is a form of this. Many bacteria pick up antibiotic resistance from lateral gene transfer.

8. Genes & Variation What is the relationship between genotype & phenotype? The genotype determines the phenotype.

9. Genes & Variation What is a single-gene trait? 1.A trait determined by a single gene that has two alleles. 2.There can only be two or three different phenotypes. 2 = complete dominance 3 = incomplete or codominance

10. Genes & Variation What is a polygenic trait? 1.A trait controlled by two or more genes. 2.Produces many possible phenotypes. 3.The range of phenotypes typically creates a bell-shaped curve (normal distribution). 4.Human height & skin color are two examples of a polygenic trait.

11. Evolution as Genetic Change Does natural selection act directly on genes? No Why? Natural selection works directly on the entire organism. What is an adaptation? Genetically controlled trait that increases fitness.

12. Evolution as Genetic Change Natural Selection on single-gene traits can lead to changes in allele frequencies, and thus evolution.

13. Evolution as Genetic Change Natural Selection on Polygenic Traits: 1.Phenotype range creates a bell-shaped curve. 2.Fitness can vary from one end of the curve to the other end.

14. Evolution as Genetic Change There are three ways in which natural selection can affect phenotype distribution: 1.Directional Selection 2.Stabilizing Selection 3.Disruptive Selection

15. Evolution as Genetic Change What is directional selection? 1.One end of the distribution curve has higher fitness. 2.Selection against one of the extremes. 3.The range of phenotypes will shift.

16. Evolution as Genetic Change What is stabilizing selection? 1.The individuals in the center of the curve has higher fitness. 2.Selection against the extreme phenotypes at both ends of the curve.

17. Evolution as Genetic Change What is disruptive (diversifying) selection? 1.Both of the extreme phenotypes have higher fitness. 2.The average phenotype is selected against.

18. Evolution as Genetic Change What is genetic drift? The random change in allele frequency within a small population.

19. Evolution as Genetic Change What is the founder effect? A change in allele frequencies as a result of migration.

20. Evolution as Genetic Change What is the Hardy-Weinberg Principle? 1.It is a model in which no evolution occurs. 2. No evolution = genetic equilibrium - no change in allele frequencies 3.This never really occurs in nature, but it helps science understand how evolution occurs.

21. Evolution as Genetic Change What are the five conditions for genetic equilibrium? 1.Large Population (no genetic drift) 2.Random Mating (no sexual selection) 3.No Immigration or Emigration (no gene flow) 4. No Mutations (no new alleles) 5.No Natural Selection (all traits aid fitness)

22. Evolution as Genetic Change How is the Hardy-Weinberg Principle expressed mathematically? p 2 + 2pq + q 2 = 1 p = frequency of one allele q = frequency of the other allele p 2 = frequency of homozygous dominant 2pq = frequency of heterozygous q 2 = frequency of homozygous recessive p + q = 1 This formula can be used to calculate changes in allele frequencies. Demo Question

23. Speciation What is a species? A group of organisms that breed with each other and produce fertile offspring. What is speciation? 1.The process that creates new species. 2.The key part of the process is reproductive isolation.

24. Speciation What are the three types of reproductive isolation? 1.Behavioral Isolation 2.Geographical Isolation 3.Temporal Isolation

25. Speciation What is behavioral isolation? Mating rituals and/or other strategies keep populations from interbreeding.

26. Speciation What is geographic isolation? A geographic barrier keeps populations from interbreeding.

27. Speciation What is temporal isolation? The populations don’t mate at the same time.

28. Speciation Speciation in Darwin’s Finches: 1.Founders arrive on the Galapagos 2.Separation of populations 3.Changes in the gene pools of each population 4.Reproductive Isolation 5.Ecological Competition 6.Continued Evolution

29. Section 19-3: Early Earth’s History

30. Earth’s Early History Formation of the Earth Geologic evidence shows Earth = 4.6 Billion years old Not “born” in a single event; cosmic collisions attracted & accumulated elements; arranged by density Early atmosphere = hydrogen cyanide, CO 2, CO, N 2, hydrogen sulfide, H 2 O vapor

31. Evolution of Life Concept Map Evolution of Life Early Earth was hot; atmosphere contained poisonous gases. (4.6 BYA) Earth cooled and oceans condensed. (3.8 BYA) Simple organic molecules may have formed in the oceans.. Small sequences of RNA may have formed and replicated. First prokaryotes may have formed when RNA or DNA was enclosed in microspheres. Later prokaryotes were photosynthetic and produced oxygen. An oxygenated atmosphere capped by the ozone layer protected Earth. First eukaryotes may have been communities of prokaryotes. Multicellular eukaryotes evolved. Sexual reproduction increased genetic variability, hastening evolution.

32. Earth’s Early History The First Organic Molecules Stanley Miller & Harold Urey set up an experiment to simulate early Earth conditions to see how organic molecules (building blocks of life) formed. Filled sterile flask with a mixture of gases found in early atmosphere; sparked with electricity to simulate lightning Results: amino acids (building blocks of protein formed); Suggests how mixtures necessary for life could have arisen from compounds present on primitive Earth.

33. Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Condensation chamber Cold water cools chamber, causing droplets to form Water vapor Liquid containing amino acids and other organic compounds Miller-Urey Experiment

34. Earth’s Early History The Puzzle of Life’s Origin: How might cells have arisen? Under certain conditions, large organic molecules can form tiny bubbles called proteinoid microspheres which have some cellular characteristics: 1.Selectively permeable membranes 2.Simple means to store/release energy

35. The Puzzle of Life’s Origins Evolution of RNA & DNA (See Fig 17-10, pg 425) Scientists don’t know how these molecules evolved, but under certain conditions, RNA can help DNA replicate Experiments show that small sequences of RNA could have formed & replicated on their own in the early Earth conditions, so scientists think RNA evolved before DNA

36. Evolution of Prokaryotes & Free Oxygen 1.Microfossils, or microscopic fossils of unicellular prokaryotes that resemble modern bacteria have been found in rocks > 3.5 billion years old! They were anaerobic since Earth’s 1 st atmosphere contained little oxygen These photosynthetic bacteria, called cyanobacteria, evolved in shallow seas; they released O 2 which accumulated in the atmosphere & removed iron from the oceans O 2 drove some life forms to extinction, while new ones evolved

37. Photosyntheis Equation

38. Recall: Prokaryotes Single-celled Lack membrane- bound organelles Lack nucleus but have DNA Also called “bacteria”

39. Recall: Eukaryotes Larger Complex internal membranes DNA enclosed within a nucleus Most have mitochondria Some have chloroplasts

40. Evolution Eukaryotic Cells About 2 billion years ago, prokaryotes began evolving internal cell membranes (ancestor of eukaryotes)

41. Origin of Mitochondrion & Chloroplasts ( Endosymbiotic Theory ) Endosymbiotic Theory – American biologist Lynn Margulis proposed this theory that states: 1.Mitochondria are descendants of symbiotic aerobic bacteria 2.Chloroplasts are descendents of symbiotic, photosynthetic bacteria

42. Origin of Mitochondrion & Chloroplasts (Endosymbiotic Theory) 3.Bacteria entered larger cells as parasites/undigested prey; they began to live inside the host where they performed either cellular respiration (mitochondria) or photoysnthesis (chloroplasts) 4.Explains why mitochondria & chloroplasts have their own DNA

43. Aerobic bacteria Ancient Prokaryotes Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Primitive Photosynthetic Eukaryote Chloroplast Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Plants and plantlike protists Animals, fungi, and non-plantlike protists Endosymbiotic Theory

44. Observations Supporting the Endosymbiotic Theory 1.Size & Structure – mitochondria are about the same size as most bacteria & its membrane is like that of aerobic bacteria 2.Genetic material- mitochondria & chloroplasts have circular DNA similar to bacterial DNA & genes different from nuclear DNA 3.Ribosomes in mitochondria & chloroplasts have similar size & structure of bacterial DNA 4.Reproduction- Like bacteria, mitochondria & chloroplasts reproduce by binary fission; Takes place independently of cell cycle of the host cell