Biology Eighth Edition Neil Campbell and Jane Reece

Transcription

1 BIG IDEA I The process of evolution drives the diversity and unity of life. Enduring Understanding 1.A Change in the genetic makeup of a population over time is evolution. Essential Knowledge 1.A.1 Natural selection is a major mechanism of evolution. PowerPoint Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

2 Essential Knowledge 1.A.1: Natural selection is a major mechanism of evolution. Learning Objectives: (1.1) The student is able to convert a data set from a table of numbers that reflect a change in the genetic makeup of a population over time and to apply mathematical methods and conceptual understandings to investigate the cause(s) and effect(s) of this change. (1.2) The student is able to evaluate evidence provided by data to qualitatively and quantitatively investigate the role of natural selection in evolution. (1.3) The student is able to apply mathematical methods to data from real or simulated populations to predict what will happen to the population in the future.

3 Overview: Endless Forms Most Beautiful A new era of biology began in 1859 when Charles Darwin published On The Origin of Species By Means of Natural Selection The Origin of Species focused biologists attention on the great diversity of organisms, whereby Darwin noted that current species are descendants of ancestral species Evolution can be defined by Darwin s phrase descent with modification, and can be viewed as both a pattern and a process

4 Darwin s Two Major Points from Origin of Species 1. The manuscript presented evidence that many species of organisms presently inhabiting the Earth are descendants of ancestral species (common descent) 2. The manuscript proposed a mechanism for the evolutionary process (natural selection) a population s allele frequency can change over generations if individuals that possess certain heritable traits leave more offspring than others results in evolutionary adaptation accumulation of inherited characteristics that enhance organisms ability to survive and reproduce in specific environments evolution change over time in genetic composition of a population and could eventually lead to new species

5 According to Darwin s theory of natural selection, competition for limited resources results in differential survival. Individuals with more favorable phenotypes are more likely to survive and produce more offspring, thus passing traits to subsequent generations.

6 Fig. 22-UN1 Observations Individuals in a population vary in their heritable characteristics. Organisms produce more offspring than the environment can support. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals and Over time, favorable traits accumulate in the population.

7 Evolutionary fitness is measured by reproductive success. FITNESS is measured as REPRODUCTIVE success. Natural selection is differential success in reproduction - it results from the interaction between individuals that vary in heritable traits and their environment.

8 Genetic variation and mutation play roles in natural selection. A diverse gene pool is important for the survival of a species in a changing environment. Two processes, mutation and sexual reproduction, produce the variation in gene pools that contributes to differences among individuals: Variation in individual genotype leads to variation in individual phenotype. Not all phenotypic variation is heritable. Natural selection can only act on variation with a genetic component.

9 Fig (a) (b)

10 Mutation Mutations are changes in the nucleotide sequence of DNA Mutations cause new genes and alleles to arise Only mutations in cells that produce gametes can be passed to offspring A A A A A A A A A a A A A a a A a A T = 0 T = 1

11 Point Mutations A point mutation is a change in one base in a gene The effects of point mutations can vary: Mutations in noncoding regions of DNA are often harmless Mutations in a gene might not affect protein production because of redundancy in the genetic code Mutations that result in a change in protein production are often harmful Mutations that result in a change in protein production can sometimes increase the fit between an organism and the environment

12 Types of Point Mutations

13 Mutations That Alter Gene Number or Sequence Chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful: Duplication of large chromosome segments is usually harmful. Duplication of small pieces of DNA is sometimes less harmful and increases the genome size. Duplicated genes can take on new functions by further mutation.

14 Types of Chromosomal Mutations

15 Sexual Reproduction Sexual reproduction can shuffle existing alleles into new combinations. In organisms that reproduce sexually, recombination of alleles is more important than mutation in producing the genetic differences that make adaptation possible. Three mechanisms contribute to the shuffling of alleles during sexual reproduction: Crossing over Independent assortment of alleles Fertilization

16 Environments can be more or less stable, and this affects evolutionary rate and direction. Different genetic variations can be selected in each generation.

17 An adaptation is a genetic variation that is favored by natural selection. It is manifested as a trait that provides an advantage to an organism in a particular environment.

18 Natural Selection: A Summary 1. Overpopulation - more organisms are born than can survive 2. Variation within a population - there will be many variation for different traits among individuals 3. Competition within the population - individuals will compete for survival: food, mates, shelter, etc. 4. Survival of the Fittest - those with traits best suited to the environment will be more likely to survive 5. Reproduction - individuals that survive will pass their traits on to the next generation 6. Adaptive Evolution over time, specialized traits that enhance survival and reproduction accumulate in a population.

19 In addition to natural selection, chance and random events can influence the evolutionary process, especially for small populations. Natural selection is NOT the only mechanism responsible for evolution. Although natural selection is usually the major mechanism for evolution, genetic variation in populations can occur through other processes: Mutation, genetic drift, sexual selection and artificial selection can all contribute to the evolution of a population. Inbreeding, small population size, nonrandom mating, the absence of migration, and a net lack of mutations can lead to loss of genetic diversity.

20 Genetic Drift The smaller a sample, the greater the chance of deviation from a predicted result. Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next. Genetic drift tends to reduce genetic variation through losses of alleles. REAL WORLD EXAMPLES OF GENETIC DRIFT: 1. The Bottleneck Effect 2. The Founder Effect

21 Fig C R C R C R C R C W C W C R C R C R C R C R C W C R C W C R C R C R C R C W C W C R C R C R C R C W C W C R C R C R C R C R C W C R C W C R C R C R C R C R C R C R C W C W C W C R C R C R C R C R C R C R C W C R C W C R C W C R C R C R C R Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 Generation 2 p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0

22 The Hardy-Weinberg equation can be used to test whether a population is evolving. Mathematical approaches are used by scientists to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population. A population is a localized group of individuals capable of interbreeding and producing fertile offspring. A gene pool consists of all the alleles for all loci in a population. A locus is fixed if all individuals in a population are homozygous for the same allele.

23 Genetic Equilibrium and Hardy-Weinberg Hardy-Weinberg Principle states that allele frequencies tend to remain constant in populations unless something happens OTHER THAN Mendelian segregation and sexual recombination. This situation in which allele frequencies remain constant is called genetic equilibrium. If allele frequencies do not change, the population will not evolve! Hardy-Weinberg is a mathematical model that describes the changes in allele frequencies in a population: Allows us to predict allele and genotype frequencies in subsequent generations (testable). Allows us to determine whether or not a population is evolving (mathematically supported evidence of evolution).

24 Calculating Allele Frequencies By convention, if there are 2 alleles at a locus, p and q are used to represent their frequencies p = frequency of dominant allele in population q = frequency of recessive allele in population The frequency of all alleles in a population will add up to 1 For example, p + q = 1

25 Model Assumptions and the Hardy-Weinberg Principle Model Assumptions: conditions required to maintain genetic equilibrium (no evolution) from generation to generation: 1. Randomly Mating Population 2. Large Population Size (n>100)/no Genetic Drift 3. No Immigration or Emigration/Restrict Gene Flow 4. No Mutations 5. No Natural Selection

26 Variables of the Hardy-Weinberg Equation Let p= frequency of the dominant allele Let q= frequency of the recessive allele Let p 2 = frequency of the homozygous dominant genotype Let 2pq= frequency of the heterozygous genotype Let q 2 = frequency of homozygous recessive genotype Law says, given assumptions, that within 1 generation of random mating, the genotype frequencies are found to be in the binomial distribution p 2 +2pq+q 2 =1 (genotype frequencies) and p+q=1 (allele frequencies)

27 Application of the Hardy-Weinberg Equilibrium Equation The allele for the ability to roll one s tongue is dominant (R) over the allele for the lack of this ability (r). In a population of 500 individuals, 25% show the recessive phenotype. How many individuals would you expect to be homozygous dominant and heterozygous? The equation: p 2 + 2pq + q 2 = 1 Therefore, p + q = 1

28 Graphical Analysis of Allele Frequencies in a Population

29 BIG IDEA I The process of evolution drives the diversity and unity of life. Enduring Understanding 1.A Change in the genetic makeup of a population over time is evolution. Essential Knowledge 1.A.2 Natural selection acts on phenotypic variations in populations. PowerPoint Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

30 Essential Knowledge 1.A.2: Natural selection acts on phenotypic variations in populations. Learning Objectives: (1.4) The student is able to evaluate data-based evidence that describes evolutionary changes in the genetic makeup of a population over time. (1.5) The student is able to connect evolutionary changes in a population over time to a change in the environment.

31 Environments change and act as selective mechanisms on populations. The environment is always changing, there is no perfect genome, and therefore a diverse gene pool is necessary for the long-term survival of species. Genetic variations within a population contribute to the diversity of the gene pool. Changes in genetic information may be silent, or result in a new phenotype (positive, negative or neutral). The interaction of the environment and the phenotype determines the fitness of the phenotype. Thus, the environment does NOT direct changes in DNA, but acts upon existing that occur through random changes in DNA.

32 Phenotypic variations ARE NOT directed by the environment but occur through RANDOM changes in the DNA and through new gene combinations. Natural selection does not create new traits, but edits or selects for traits already present in the population. The local environment determines which traits will be selected for or selected against in any specific population. Because environments change, they act as selective mechanisms on populations. Illustrative Example: peppered moth

33 Illustrative Example: The Peppered Moth

34 Some phenotypic variations significantly increase or decrease fitness of the organism and the population. Illustrative Examples: Peppered Moth DDT Resistance in Insects Sickle Cell Anemia

35 Evolution of Insecticide Resistance 1. By spraying crops with poisons to kill insects, humans have unwittingly favored the reproductive success of insects with inherent resistance to poisons. 2. Resistant individuals survive and reproduce, passing the gene for resistance to offspring. 3. Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow. READ ARTICLE: The Exterminator- Pesticides & Resistance

36 Evolution of Sickle Cell Anemia Red blood cells are able to transport oxygen because they are filled with a protein called hemoglobin, which picks up oxygen in the lungs and drops it off where it is needed in tissues and organs. A mutated version in one of the hemoglobin genes leads to Sickle Cell Anemia by changing the hemoglobin protein in such a way that it tends to clump up into long chains inside red blood cells. Instead of maintaining the usual flexible disc-like shape that enables them to squeeze through even the tiniest blood vessels, the red blood cells of people with the disease twist into stiff crescents that are not efficient at transporting oxygen. "Sickled" red blood cells can clog small blood vessels, preventing oxygen from making it to certain parts of the body. The condition is life-threatening. READ ARTICLE: Heterozygous Advantage & Sickle Cell Anemia

37 Molecular Basis of Sickle Cell Disease In the DNA, the mutant template strand (top) has an A where the wild type template has a T. The mutant mrna has a U instead of an A in one codon. The mutant (sickle cell) hemoglobin has a valine (Val) instead of a glutamic acid (Glu). This mutation causes the hemoglobin protein to be inproperly shaped.

38 Heterozygous Advantage & Sickle Cell Anemia In the United States, one in every 500 African-American births and one out of every 1,000 to 1,400 Hispanic births is affected by Sickle Cell Anemia. Another two million Americans carry the sickle cell trait. As devastating as the disease can be, it turns out there is a reason Sickle Cell Anemia is so common and has NOT been weeded out of the human population. Usually a DNA change that causes a serious disease quickly gets pushed out of a population's gene pool. But researchers have found that the version of the gene that causes Sickle Cell Anemia has been around for thousands of years. That observation, and the fact that this version is mainly found in people with ancestors who lived relatively recently in Africa, the Mediterranean, India, or the Middle East, led scientists to wonder if the Sickle Cell Anemia-causing version of the gene offers some kind of benefit to people living in those regions.

39 Nevertheless, carriers are not completely protected from the disease and experts recommend that they still take precautions against malaria. Sickle Cell and Resistance to Malaria That benefit turned out to be resistance to malaria. Malaria is caused by parasites that multiply inside of human red blood cells. Because the disease can only be transferred from person to person by mosquitoes, it is confined to areas of the world where the insects thrive. Every year malaria infects more than 300 million people and kills more than a million, particularly young children. Carriers of the sickle cell trait are to a large extent resistant to malaria. Compared to non-carriers, they have approximately 1/10 the risk of dying from infection by the most deadly species of malaria parasite.

40 Heterozygous Advantage & Sickle Cell Anemia Over the years, carriers living in malaria-ridden locales would have had a survival benefit compared to noncarriers, allowing them to live longer and have more children. This benefit is what evolutionary biologists call "heterozygote advantage," and it explains why the sickle cell trait has persisted in areas where malaria is common. The price for the carriers' advantage, though, is that some of their children are born with Sickle Cell Anemia.

41 Fig Mapping Malaria & Sickle Cell Disease Frequencies of the sickle-cell allele 0 2.5% Distribution of malaria caused by Plasmodium falciparum (a parasitic unicellular eukaryote) % % % % >12.5%

42 Humans impact variation in other species. Illustrative Examples: Artificial Selection Overuse of Antibiotics

43 Fig Terminal bud Lateral buds Cabbage Flower clusters Brussels sprouts Leaves Cauliflower Kale Stem Broccoli Wild mustard Flowers and stems Kohlrabi

44 Human Impact on Genetic Variation

45 Fig. 22-UN2 INQUIRY CHALLENGE Mosquitoes resistant to the pesticide DDT first appeared in India in 1959, but now are found throughout the world. a. Graph the data in the table above. b. Examine the graph and hypothesize why the percentage of mosquitoes resistant to DDT rose rapidly. c. Suggest an explanation for the global spread of DDT resistance.

46 Fig. 22-UN3

47 BIG IDEA I The process of evolution drives the diversity and unity of life. Enduring Understanding 1.A Change in the genetic makeup of a population over time is evolution. Essential Knowledge 1.A.3 Evolutionary change is also driven by random processes. PowerPoint Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

48 Essential Knowledge 1.A.3: Evolutionary change is also driven by random processes. Learning Objectives: (1.6) The student is able to use data from mathematical models based on the Hardy-Weinberg equilibrium to analyze genetic drift and effects of selection in the evolution of specific populations. (1.7) The student is able to justify data from mathematical models based on the Hardy-Weinberg equilibrium to analyze genetic drift and the effects of selection in the evolution of specific populations. (1.8) The student is able to make predictions about the effects of genetic drift, migration and artificial selection on the genetic makeup of a population.

49 Remember: The process of evolution drives the diversity and unity of life. Evolution is a change in the genetic makeup of a population over time with natural selection its major driving mechanism. Darwin s theory, supported by evidence from many disciplines, states that inheritable variations occur in individuals in a population. Due to competition for limited resources, individuals with more favorable variations are more likely to survive and produce more offspring, thus passing traits to future generations. Individuals do not evolve, but rather populations evolve.

50 Remember: Natural selection is not the only mechanism responsible for evolution. Although natural selection is usually the major mechanism for evolution, genetic variation in populations can occur through other processes: Mutation, genetic drift, sexual selection and artificial selection can all contribute to the evolution of a population. Inbreeding, small population size, nonrandom mating, the absence of migration, and a net lack of mutations can lead to loss of genetic diversity.

51 Overview: The Smallest Unit of Evolution Focusing on evolutionary change in populations, we can define evolution on its smallest scale, called microevolution. Microevolution involves evolutionary changes below the species level; changes in allele frequencies in a population over generations. Our focus in this section will be to understand that natural selection is not the only cause of microevolution. The other two mechanisms include genetic drift and gene flow.

52 Genetic drift is a nonselective process occurring in small populations. The smaller a sample, the greater the chance of deviation from a predicted result. Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next. Genetic drift tends to reduce genetic variation through losses of alleles.

53 The Founder Effect Sample of Original Population Founding Population A Descendants Founding Population B

54 The Bottleneck Effect

55 Fig Pre-bottleneck (Illinois, 1820) Post-bottleneck (Illinois, 1993) (a) Range of greater prairie chicken Location Population size Number of alleles per locus Percentage of eggs hatched Illinois s 1,000 25, < <50 Kansas, 1998 (no bottleneck) 750, Nebraska, 1998 (no bottleneck) 75, , (b) Minnesota, 1998 (no bottleneck) 4,

56 Reduction of the genetic variation within a given population can increase the differences between populations of the same species. Upon arrival to Galapagos, organisms were identical to their ancestors on the mainland of S. America. Random loss of genetic variation over time increased the differences between the island dwellers and their ancestors.

57 Effects of Genetic Drift: A Summary 1. Genetic drift is significant in small populations 2. Genetic drift causes allele frequencies to change at random 3. Genetic drift can lead to a loss of genetic variation within populations 4. Genetic drift can cause harmful alleles to become fixed 5. Genetic drift can facilitate inbreeding which leads to further reduction in variation

58 Natural selection is the only mechanism that consistently causes adaptive evolution. Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions. Only natural selection consistently results in adaptive evolution! Natural selection brings about adaptive evolution by acting on an organism s phenotype, NOT genotype. The phrases struggle for existence and survival of the fittest are misleading as they imply direct competition among individuals, BUT reproductive success is generally more subtle and depends on many factors. Natural selection occurs in three ways: stabilizing selection, directional selection, and disruptive selection.

59 Directional, Disruptive, and Stabilizing Selection Three modes of selection: Directional selection favors individuals at one end of the phenotypic range Disruptive selection favors individuals at both extremes of the phenotypic range Stabilizing selection favors intermediate variants and acts against extreme phenotypes

60 Fig a Original population Phenotypes (fur color) Original population Evolved population (a) Directional selection

61 Fig b Original population Phenotypes (fur color) Evolved population (b) Disruptive selection

62 Fig c Original population Phenotypes (fur color) Evolved population (c) Stabilizing selection

63 The Key Role of Natural Selection in Adaptive Evolution Natural selection increases the frequencies of alleles that enhance survival and reproduction. Adaptive evolution occurs as the match between an organism and its environment increases. Because the environment can change, adaptive evolution is a continuous process. Genetic drift does not consistently lead to adaptive evolution as they can increase or decrease the match between an organism and its environment.

64 BIG IDEA I The process of evolution drives the diversity and unity of life. Enduring Understanding 1.A Change in the genetic makeup of a population over time is evolution. Essential Knowledge 1.A.4 Biological evolution is supported by scientific evidence from many disciplines, including mathematics. PowerPoint Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

65 Essential Knowledge 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics. Learning Objectives: (1.9) The student is able to evaluate evidence provided by data from many scientific disciplines that support biological evolution. (1.10) The student is able to refine evidence based on data from many scientific disciplines that support biological evolution. (1.11) The student is able to design a plan to answer scientific questions regarding how organisms have changed over time using information from morphology, biochemistry and geology. (1.12) The student is able to connect scientific evidence from many disciplines to support the modern concept of evolution. (1.13) The student is able to construct and/or justify mathematical models, diagrams or simulations that represent processes of biological evolution.

66 Direct Evidence for Evolution Evolution is supported by an overwhelming amount of scientific evidence from geographical, geological, physical, chemical and mathematical applications. New discoveries continue to fill the gaps identified by Darwin in The Origin of Species. Two examples provide direct evidence for natural selection: 1. the effect of differential predation on guppy populations; 2. and the evolution of drug-resistant HIV

67 Number of colored spots Fig EXPERIMENT Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Guppies: Adult males have brighter colors than those in pike-cichlid pools Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in killifish pools RESULTS Source Transplanted population population 8 2 Source population Transplanted population

68 The Evolution of Drug-Resistant HIV The use of drugs to combat HIV selects for viruses resistant to these drugs HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus

69 Fig Patient No. 1 Patient No Patient No Weeks

70 Evidence for Evolution Evidence that the diversity of life is a product of evolution pervades every research field of biology. Molecular, morphological and genetic information of existing and extinct organisms add to our understanding of evolution: Fossil Record Evidence Succession of Fossil Forms Comparative Anatomy Biogeography Anatomical Homologies Embryological Homologies Molecular Homologies Geographic Distribution of Species Continental Drift

71 Evidence for Evolution

72 How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils: In relative dating, the order of rock strata is used to determine the relative age of fossils. Older specimens are found in deeper layers of strata. The absolute ages of fossils can be determined by radiometric dating Radiometric dating uses the decay of radioactive isotopes to determine the age of the rocks or fossils. It is based on the rate of decay, or half-life of the isotope (the time required for half the parent isotope to decay).

73 Fig Morphological Homologies Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat Homologous structures are those found in different species that are similar and result from common ancestry.

74 Fig Comparative Embryology Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo

75 Vestigial Structures The skeletons of some snakes retain vestiges of the pelvis and leg bones of walking ancestors. We would not expect to see these structures if snakes had an origin separate from other vertebrate animals.

76 Molecular Homologies

77 Convergent Evolution Although organisms that are closely related share characteristics because of common descent, distantly related organisms can resemble one another for a different reason: Convergent evolution is the evolution of similar, or analogous, features in distantly related groups. Analogous traits arise when groups independently adapt to similar environments in similar ways. Convergent evolution does not provide information about ancestry!

78 Homologous v. Analogous Structures Homologous structures are similar structures occurring in different species that are believed to be derived from a common ancestor. Analogous structures are similar structures occurring in different species that are believed to be the result of convergent evolution (similar environmental pressures).

79 Fig Sugar glider NORTH AMERICA AUSTRALIA Flying squirrel

80 Biogeography: The Geographic Distribution of Species