Microevolution. Chapter 17

Transcription

1 Microevolution Chapter 17

2 Selective Breeding & Evolution Evolution is genetic change in a line of descent through successive generations Selective breeding practices yield evidence that heritable changes do occur

3 Domestication of Dogs Began about 50,000 years ago 14,000 years ago - artificial selection Dogs with desired forms of traits were bred Modern breeds are the result

4 Results of Artificial Selection Extremes in size Great Dane and Chihuahua Extremes in form Short-legged dachshunds English bulldog Short snout and compressed face Extreme traits lead to health problems

5 Evolutionary Theories Widely used to interpret the past and present, and even to predict the future Reveal connections between the geological record, fossil record, and organism diversity

6 Early Scientific Theories Hippocrates - All aspects of nature can be traced to their underlying causes Aristotle - Each organism is distinct from all the rest and nature is a continuum or organization

7 Confounding Evidence Biogeography Comparative anatomy Geologic discoveries

8 Biogeography Size of the known world expanded enormously in the 15th century Discovery of new organisms in previously unknown places could not be explained by accepted beliefs How did species get from center of creation to all these places?

9 Comparative Morphology Study of similarities and differences in body plans of major groups Puzzling patterns: Animals as different as whales and bats have similar bones in forelimbs Some parts seem to have no function

10 Geological Discoveries Similar rock layers throughout world Certain layers contain fossils Deeper layers contain simpler fossils than shallow layers Some fossils seem to be related to known species

11 19th Century - New Theories Scientists attempt to reconcile evidence of change with traditional belief in a single creation event Two examples Georges Cuvier - multiple catastrophes Jean Lamarck - inheritance of acquired characteristics

12 INITIAL QUESTION: Give an example of a species that exhibits the effects of sexual selection OBJECTIVES: Critique past evolutionary theories with present evolutionary theories. Formulate reasons to defend their analysis position. Explain why natural selection can act only on inherited traits. Apply the concept of natural selection to illustrate and account for a species' survival, extinction or change over time. Standards: 1.A.1: Natural selection is a major mechanism of evolution.

13 The Theory of Uniformity Lyell s Principles of Geology Subtle, repetitive processes of change had shaped Earth Challenged the view that Earth was only 6,000 years old

14 Darwin s Voyage At age 22, Charles Darwin began a fiveyear, round-the-world voyage aboard the Beagle In his role as ship s naturalist, he collected and examined the species that inhabited the regions the ship visited

15 Voyage of the Beagle EQUATOR Galapagos Islands Figure 17.4e Page 275

16 Galapagos Islands Darwin Wolf Volcanic islands far off coast of Ecuador All inhabitants are descended from species that arrived on islands from elsewhere Fernandia Isabela Pinta Marchena Santiago Bartolomé Rabida Pinzon Tortuga Floreana Genovesa Seymour Baltra Santa Cruz Santa Fe San Cristobal Española Figure 17.4d Page 275

17 Malthus - Struggle to Survive Thomas Malthus, a clergyman and economist, wrote essay that Darwin read on his return to England Argued that as population size increases, resources dwindle, the struggle to live intensifies, and conflict increases

18 Galapagos Finches Darwin observed finches with a variety of lifestyles and body forms On his return, he learned that there were 13 species He attempted to correlate variations in their traits with environmental challenges

19 Darwin s Theory A population can change over time when individuals differ in one or more heritable traits that are responsible for differences in the ability to survive and reproduce.

20 Alfred Wallace Naturalist who arrived at the same conclusions Darwin did Wrote to Darwin describing his views Prompted Darwin to finally present his ideas in a formal paper

21 Populations Evolve Biological evolution does not change individuals It changes a population Traits in a population vary among individuals Evolution is change in frequency of traits

22 TICKET OUT THE DOOR Explain the difference between an acquired characteristic and an inherited characteristic.

23 DO NOW: Explain the role of mutations in evolution. OBJECTIVES: Explain why natural selection can act only on inherited traits. Apply the concept of natural selection to illustrate and account for a species' survival, extinction or change over time. Describe the factors (e.g., isolation, differential reproduction) affecting gene frequency in a population over time and their consequences. STANDARDS: 1.A.1: Natural selection is a major mechanism of evolution.

24 The Gene Pool All of the genes in the population Genetic resource that is shared (in theory) by all members of population

25 Variation in Phenotype Each kind of gene in gene pool may have two or more alleles Individuals inherit different allele combinations This leads to variation in phenotype Offspring inherit genes, not phenotypes

26 What Determines Alleles in New Individual? Mutation Crossing over at meiosis I Independent assortment Fertilization Change in chromosome number or structure

27 Genetic Equilibrium Allele frequencies at a locus are not changing Population is not evolving

28 Five Conditions No mutation Random mating Gene doesn t affect survival or reproduction Large population No immigration/emigration

29 Microevolutionary Processes Drive a population away from genetic equilibrium Small-scale changes in allele frequencies brought about by: Natural selection Gene flow Genetic drift

30 Gene Mutations Infrequent but inevitable Each gene has own mutation rate Lethal mutations Neutral mutations Advantageous mutations

31 Hardy-Weinberg Rule At genetic equilibrium, proportions of genotypes at a locus with two alleles are given by the equation: p 2 AA + 2pq Aa + q 2 aa = 1 Frequency of allele A = p Frequency of allele a = q

32 Punnett Square p A q a p A AA(p 2 ) Aa(pq) q a Aa(pq) aa(q 2 ) In-text figure Page 280

33 Frequencies in Gametes F 1 genotypes: Gametes: 0.49 AA 0.42 Aa 0.09 aa A A A a a a A 0.3a In-text figure Page 280

34 STARTING POPULATION 490 AA butterflies Dark-blue wings No Change through Generations 420 Aa butterflies Medium-blue wings 90 aa butterflies White wings THE NEXT GENERATION 490 AA butterflies 420 Aa butterflies 90 aa butterflies NO CHANGE THE NEXT GENERATION 490 AA butterflies 420 Aa butterflies Figure 17.9 Page aa butterflies NO CHANGE

35 Natural Selection A difference in the survival and reproductive success of different phenotypes Acts directly on phenotypes and indirectly on genotypes

36 Reproductive Capacity & Competition All populations have the capacity to increase in numbers No population can increase indefinitely Eventually the individuals of a population will end up competing for resources

37 Variation in Populations All individuals have the same genes that specify the same assortment of traits Most genes occur in different forms (alleles) that produce different phenotypes Some phenotypes compete better than others

38 Change over Time Over time, the alleles that produce the most successful phenotypes will increase in the population Less successful alleles will become less common Change leads to increased fitness Increased adaptation to environment

39 Results of Natural Selection Three possible outcomes: A shift in the range of values for a given trait in some direction Stabilization of an existing range of values Disruption of an existing range of values

40 Round Robin Describe one item you learned from the video.

41 DO NOW: How does natural selection lead to more genetic diversity among a species? OBJECTIVES: Apply the concept of natural selection to illustrate and account for species survival, extinction, or change over time STANDARDS: 1.A.1: Natural selection is a major mechanism of evolution C D.1,2,3,4,7,8

42 in the population Number of individuals in the population Number of individuals in the population Directional Selection Allele frequencies shift in one direction Number of individuals Range of values for the trait at time 1 Range of values for the trait at time 2 Figure Page 282 Range of values for the trait at time 3

43 Peppered Moths Prior to industrial revolution, most common phenotype was light colored After industrial revolution, dark phenotype became more common

44 Pesticide Resistance Pesticides kill susceptible insects Resistant insects survive and reproduce If resistance has heritable basis, it becomes more common with each generation

45 Antibiotic Resistance First came into use in the 1940s Overuse has led to increase in resistant forms Most susceptible cells died out and were replaced by resistant forms

46 Number of individuals in the population Stabilizing Selection Intermediate forms are favored and extremes are eliminated Range of values for the trait at time 1 Range of values for the trait at time 2 Figure Page 284 Range of values for the trait at time 3

47 Selection for Gall Size Gall-making fly has two major predators Wasps prey on larvae in small galls Birds eat larvae in large galls Flies that cause intermediate-sized galls have the highest fitness

48 Number of individuals in the population Number of individuals in the population Number of individuals in the population Disruptive Selection Forms at both ends of the range of variation are favored Intermediate forms are selected against Range of values for the trait at time 1 Range of values for the trait at time 2 Figure Page 285 Range of values for the trait at time 3

49 Number of individuals African Finches Selection favors birds with very large or very small bills nestlings drought survivors Birds with intermediate-sized bill are less effective feeders Figure Page 285 Widest part of lower bill (millimeters)

50 Sexual Selection Selection favors certain secondary sexual characteristics Through nonrandom mating, alleles for preferred traits increase Leads to increased sexual dimorphism al-planet/28483-ms-adventure-thered-legged-honeycreeper-video.htm

51 Balanced Polymorphism Polymorphism - having many forms Occurs when two or more alleles are maintained at frequencies greater than 1 percent

52 Sickle-Cell Trait: Heterozygote Advantage Allele Hb S causes sickle-cell anemia when heterozygous Heterozygotes are more resistant to malaria than homozygotes Figure Page Malaria case Sickle-cell trait less than 1 in 1,600 1 in 400-1,600 1 in in in more than 1 in 64

53 Round Robin As a table Name, discuss, and describe one type of selection and provide an example of the selection type.

54 Gene Flow Physical flow of alleles into a population Tends to keep the gene pools of populations similar Counters the differences that result from mutation, natural selection, and genetic drift

55 Genetic Drift Random change in allele frequencies brought about by chance Effect is most pronounced in small populations Sampling error - Fewer times an event occurs, greater the variance in outcome

56 Computer Simulation 1.0 AA in five populations 0.5 allele A lost from four populations Generation (25 stoneflies at the start of each) Figure 17.19a Page 288

57 Computer Simulation allele A neither lost nor fixed Generation (500 stoneflies at the start of each) Figure 17.19b Page 288

58 Bottleneck A severe reduction in population size Causes pronounced drift Example Elephant seal population hunted down to just 20 individuals Population rebounded to 30,000 Electrophoresis revealed there is now no allele variation at 24 genes

59 Founder Effect Effect of drift when a small number of individuals starts a new population By chance, allele frequencies of founders may not be same as those in original population Effect is pronounced on isolated islands

60 Inbreeding Nonrandom mating between related individuals Leads to increased homozygosity Can lower fitness when deleterious recessive alleles are expressed Amish, cheetahs

61 DO NOW: If birds and mammals that are flashy and colorful attract predators, then why are they so colorful? STANDARDS: 1.A.1: Natural selection is a major mechanism of evolution C D.1,2,3,4,7,8 OBJECTIVES: Describe how evolution is evident at the population level for species. Critique past evolutionary theories with present evolutionary theories. Explain why natural selection can act only on inherited traits. Describe the factors affecting gene frequency in a population over time and their consequences. Apply the concept of natural selection to illustrate and account for a species survival, extinction or change over time. Analyze genetic drift and the effects of selection in the evolution of a population. Make predictions about the effects of genetic drift, migration, and artificial selection. Justify data from models to analyze genetic drift and the effects of selection in the evolution of specific populations