Chapter 17 Processes of Evolution Sections 1-6

1. Chapter 17Processes of EvolutionSections 1-6

2. 17.1 Rise of the Super Rats • When warfarin was used to control rats, natural selection favored individuals with a mutation in the VKORC1 gene which resulted in warfarin resistance • When warfarin resistance increased in rat populations, people stopped using warfarin to kill rats • The frequency of the warfarin-resistance allele in rat populations declined, probably because rats that carry the allele are not as healthy as ones that do not

3. Rats Infesting Rice Fields in the Philippines

4. Variation In Populations • All individuals of a species share certain morphological, physiological, and behavioral traits • Apopulationis a group of interbreeding individuals of the same species in a specified area • Individuals of a population with different alleles of shared genes vary in the details of their shared traits

5. Phenotypic Variations

6. An Evolutionary View of Mutations • Mutations are the source of new alleles that give rise to differences in details of shared traits • Lethal mutations result in death • Neutral mutationshave no effect on survival or reproduction • Beneficial mutationsconvey an advantage

7. Table 17-1 p272

8. The Gene Pool • Gene pool • All genes found in one population • Alleles • Different forms of the same gene • Determine genotype and phenotype • Dimorphism and polymorphism

9. Allele Frequencies and Microevolution • Allele frequencyrefers to the relative abundance of a particular allele of a given gene in a population • Changes in allele frequency of a population (or a species) is called microevolution • Microevolutionary processes include mutation, natural selection, genetic drift, and gene flow

10. Genetic Equilibrium • Under certain ideal conditions, the frequency of an allele in a sexually reproducing population’s gene pool should remain stable from one generation to the next • Five conditions required for a genetic equilibrium: • Mutations do not occur • Population is infinitely large • Population is isolated (no gene flow) • Mating is random • All individuals survive and reproduce equally

11. The Hardy-Weinberg Formula • The Hardy-Weinberg formula can be used to determine if a population is in genetic equilibrium p2(BB) + 2pq (Bb) + q2(bb) = 1.0 • The frequency of the dominant allele (B) plus the recessive allele (b) equals 1.0 p + q = 1.0

12. Applying the Rule • A population consists of 1,000 plants: 490 homozygous (BB), 420 heterozygous(Bb), and 90 homozygous (bb) • Each plant makes two gametes: • All gametes made by BB individuals have the B allele • All gametes made by bb individuals have the ballele • Bb individuals have half B gametes half b gametes

13. Applying the Rule • Frequency of the B allele: p (B) = (980 + 420) ÷ 2,000 = 1,400 ÷ 2,000 = 0.7 • Frequency of the b allele: q (b) = (180 + 420) ÷ 2,000 = 600 ÷ 2,000 = 0.3

14. Natural Selection • Natural selectionresults from the differential survival and reproduction among individuals of a population that vary in details of their shared traits • Natural selection occurs in three recognizable patterns depending on the organisms and their environment: • Directional selection • Stabilizing selection • Disruptive selection

15. 17.5 Directional Selection • Changing environmental conditions can result in a directional shift in allele frequencies • Directional selection • Changing environmental conditions can shift allele frequencies in a consistent direction • Forms of traits at one end of a range of phenotypic variation become more common

16. Number of individuals in population Time 1 Range of values for the trait Time 2 Time 3 Stepped Art Figure 17-5 p276

17. Directional Selection in Peppered Moths • In preindustrial England, most moths were light-colored, and a dominant allele that resulted in darker coloration was rare • In post-industrial England, pollution from coal-burning factories changed the colors of the forests • Predatory birds ate more light-colored moths in soot-darkened forests, and more dark-colored moths in clean forests • Light color is adaptive in areas of low pollution; dark color is adaptive in areas of high pollution

18. Directional Selection in Peppered Moths

19. Directional Selection in Rock-Pocket Mice • In rock-pocket mice, two alleles of a single gene control coat color • Night-flying owls are the selective pressure that directionally shifts the allele frequency • Most of the mice in populations that inhabit dark rock have dark gray coats • Most of the mice in populations that inhabit light brown rock have light brown coats

20. Directional Selection in Rock-Pocket Mice

21. Directional Selection in Rock-Pocket Mice

22. Directional Selection in Antibiotic Resistant Bacteria • A typical two-week course of antibiotics can exert selection pressure on over a thousand generations of bacteria • Antibiotics are used preventively in humans, cattle, pigs, chickens, fish, and other animals raised on factory farms • Bacteria with alleles that allow them to survive antibiotic treatment (antibiotic resistant strains) are now common in hospitals and schools

23. Take-Home Message: What is the effect of directional selection? • Directional selection causes allele frequencies underlying a range of variation to shift in a consistent direction

24. 17.6 Stabilizing and Disruptive Selection • Stabilizing selection • Natural selection that favors an intermediate phenotype and eliminates extreme forms • Disruptive selection • Natural selection that favors extreme forms of a trait and eliminates the intermediate forms

25. Number of individuals in population Time 1 Range of values for the trait Time 2 Time 3 Stepped Art Figure 17-8 p278

26. Number of individuals in population Time 1 Range of values for the trait Time 2 Time 3 Stepped Art Figure 17-10 p279

27. Take-Home Message: Natural selection can favor intermediate or extreme forms of traits • With stabilizing selection, an intermediate phenotype is favored, and extreme forms are selected against • With disruptive selection, an intermediate form of a trait is selected against, and extreme phenotypes are favored

28. Chapter 17Processes of EvolutionSections 7-12

29. Sexual Selection: Birds of Paradise

30. Sexual Selection: Stalk-Eyed Flies

31. Balanced Polymorphism • Balanced polymorphism • A state in which natural selection maintains two or more alleles at relatively high frequencies • Occurs when environmental conditions favor heterozygotes • Example: Sickle cell anemia and malaria • Mosquitoes transmit the parasitic protist that causes malaria, Plasmodium, to human hosts • HbA/HbS heterozygotes survive malaria more often than people who make only normal hemoglobin

32. Take-Home Message: How does natural selection maintain diversity? • With sexual selection, a trait is adaptive if it gives an individual an advantage in securing mates • Sexual selection reinforces phenotypical differences between males and females, and sometimes gives rise to exaggerated traits • Environmental pressures that favor heterozygotes can lead to a balanced polymorphism

33. Genetic Drift • Genetic drift • A random change in allele frequencies over time • Can lead to a loss of genetic diversity, especially in small populations • When all individuals of a population are homozygous for an allele, that allele is fixed

34. Bottlenecks • Bottleneck • A drastic reduction in population size brought about by severe pressure • After a bottleneck, genetic drift is pronounced when a few individuals rebuild a population • Example: Northern elephant seals

35. The Founder Effect • Founder effect • Genetic drift is pronounced when a few individuals start a new population • Inbreeding • Breeding or mating between close relatives who share a large number of alleles • Example: Old Order Amish in Lancaster County, Pennsylvania (Ellis-van Creveld syndrome)

36. Gene Flow • Gene flow • Physical movement of alleles caused by individuals moving into and away from populations • Tends to counter the evolutionary effects of mutation, natural selection, and genetic drift on a population • Example: Movement of acorns by blue jays allows gene flow between oak populations

37. Take-Home Message: How does a population’s genetic diversity become reduced? • Genetic drift, or random change in allele frequencies, can reduce a population’s genetic diversity; its effect is greatest in small populations, such as one that endures a bottleneck • Gene flow is the physical movement of alleles into and out of a population; it tends to counter the evolutionary effects of mutation, natural selection, and genetic drift

38. 17.9 Reproductive Isolation • Speciation differs in its details, but reproductive isolating mechanisms are always part of the process • Speciation • Evolutionary process by which new species form • Reproductive isolating mechanisms are always part of the process • Reproductive isolation • The end of gene exchange between populations • Beginning of speciation

39. Reproductive Isolating Mechanisms • Reproductive isolating mechanisms prevent interbreeding among species • Heritable aspects of body form, function, or behavior that arise as populations diverge • Prezygotic isolating mechanisms prevent pollination or mating • Postzygotic isolating mechanisms result in weak or infertile hybrids

40. Prezygotic Isolating Mechanisms • With temporal isolation populations can’t interbreed because the timing of their reproduction differs • With mechanical isolation, the size or shape of an individual’s reproductive parts prevent it from mating with members of another population

41. Figure 17-17a p285

42. Figure 17-17b p285

43. Prezygotic Isolating Mechanisms (cont.) • Populations adapted to different microenvironments in the same region may be ecologically isolated • In animals, behavioral differences can stop gene flow between related species (behavioral isolation) • In gamete incompatibility, gametes of different species meet but have molecular incompatibilities that prevent a zygote from forming

44. Postzygotic Isolation Mechanisms • Hybrid inviability • Extra or missing genes, or incompatible gene products • Offspring may be inviable, or have reduced fitness (ligers, tigons) • Hybrid sterility • Some interspecies crosses produce robust but sterile offspring (e.g. mules) • Fertile offspring may have lower fitness with successive generations

45. Different species form and . . . Prezygotic reproductive isolation Individuals reproduce at different times (temporal isolation). Physical incompatibilities prevent individuals from interbreeding (mechanical isolation). Individuals live in different places so they never meet up for sex (ecological isolation). Individuals ignore or do not get the required cues for sex (behavioral isolation). Mating occurs and . . . No fertilization occurs (gamete incompatibility). Zygotes form and . . . Postzygotic reproductive isolation Hybrid embryos die early, or new individuals die before they can reproduce (hybrid inviability). Hybrid individuals or their offspring do not make functional gametes (hybrid sterility). Interbreeding is successful Stepped Art Figure 17-16 p284

46. Take-Home Message: How do species attain and maintain separate identities? • Speciation is an evolutionary process by which new species form; it varies in its details and duration • Reproductive isolation, which occurs by one of several mechanisms, is always a part of speciation

47. 17.10 Allopatric Speciation • In allopatric speciation a physical barrier arises and ends gene flow between populations • Genetic divergence results in speciation • Example: Geographic isolation of Atlantic and Pacific species caused by the formation of the Isthmus of Panama

48. Allopatric Speciation on an Archipelago

49. Sympatric Speciation • In sympatric speciation, new species form within a home range of an existing species, in the absence of a physical barrier • Sympatric speciation can occur in a single generation when the chromosome number multiplies (polyploidy) • Example: Common bread wheat originated after related species hybridized, then the chromosome number of the hybrid offspring doubled

50. Sympatric Speciation in Wheat Triticum turgidum (emmer) Aegilops tauschii (goatgrass) Aegilops (wild goatgrass, unknown species) Triticum (hybrid) Triticum urartu (wild einkorn) Triticum aestivum (bread wheat) 14 AA X 14 BB 14 AB 28 AABB X 14 DD 42 AABBDD