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Chapter 21 Active Reading Guide: the Evolution of Populations

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Biology in Focus - Chapter 21

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Biology in Focus - Chapter 21 - Development of Populations

Biology in Focus - Chapter 21 - Evolution of Populations

  1. 1. CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry • Cain • Wasserman • Minorsky • Jackson • Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 21 The Evolution of Populations
  2. 2. © 2014 Pearson Instruction, Inc. Overview: The Smallest Unit of measurement of Evolution  I mutual misconception is that organisms evolve during their lifetimes  Natural option acts on individuals, but only populations evolve  Consider, for example, a population of medium ground finches on Daphne Major Isle  During a drought, large-beaked birds were more than probable to scissure large seeds and survive  The finch population evolved past natural selection
  3. 3. © 2014 Pearson Instruction, Inc. Figure 21.ane
  4. 4. © 2014 Pearson Education, Inc. Figure 21.two 1978 (later drought) 10 1976 (like to the prior iii years) Averagebeakdepth(mm) ix 8 0
  5. five. © 2014 Pearson Education, Inc.  Microevolution is a change in allele frequencies in a population over generations  Iii mechanisms cause allele frequency change  Natural selection  Genetic drift  Gene flow  Only natural pick causes adaptive evolution
  6. six. © 2014 Pearson Education, Inc.  Variation in heritable traits is a prerequisite for evolution  Mendel's work on pea plants provided evidence of discrete heritable units (genes) Concept 21.1: Genetic variation makes development possible
  7. vii. © 2014 Pearson Didactics, Inc. Genetic Variation  Phenotypic variation oft reflects genetic variation  Genetic variation among individuals is caused by differences in genes or other DNA sequences  Some phenotypic differences are due to differences in a single gene and can be classified on an "either- or" basis  Other phenotypic differences are due to the influence of many genes and vary in gradations along a continuum
  8. 8. © 2014 Pearson Instruction, Inc. Figure 21.3
  9. 9. © 2014 Pearson Education, Inc.  Genetic variation can be measured at the whole gene level equally gene variability  Gene variability can exist quantified as the average pct of loci that are heterozygous
  10. 10. © 2014 Pearson Education, Inc.  Genetic variation can exist measured at the molecular level of DNA as nucleotide variability  Nucleotide variation rarely results in phenotypic variation  Most differences occur in noncoding regions (introns)  Variations that occur in coding regions (exons) rarely change the amino acid sequence of the encoded protein
  11. 11. © 2014 Pearson Education, Inc. Figure 21.4 one,000 Exchange resulting in translation of different amino acid Base-pair substitutions Insertion sites Deletion Exon Intron 1 500 2,5002,0001,500
  12. 12. © 2014 Pearson Education, Inc.  Phenotype is the product of inherited genotype and environmental influences  Natural option can only human activity on phenotypic variation that has a genetic component
  13. 13. © 2014 Pearson Didactics, Inc. Figure 21.5 (a) Caterpillars raised on a diet of oak flowers (b) Caterpillars raised on a diet of oak leaves
  14. 14. © 2014 Pearson Teaching, Inc. Figure 21.5a (a) Caterpillars raised on a nutrition of oak flowers
  15. 15. © 2014 Pearson Education, Inc. Figure 21.5b (b) Caterpillars raised on a diet of oak leaves
  16. sixteen. © 2014 Pearson Didactics, Inc. Sources of Genetic Variation  New genes and alleles tin arise by mutation or gene duplication
  17. 17. © 2014 Pearson Education, Inc. Formation of New Alleles  A mutation is a change in the nucleotide sequence of DNA  Only mutations in cells that produce gametes tin can be passed to offspring  A "point mutation" is a change in one base of operations in a gene
  18. 18. © 2014 Pearson Pedagogy, Inc.  The effects of signal mutations tin vary  Mutations in noncoding regions of DNA are often harmless  Mutations to genes can be neutral because of back-up in the genetic code
  19. 19. © 2014 Pearson Educational activity, Inc.  The effects of point mutations can vary  Mutations that alter the phenotype are frequently harmful  Mutations that outcome in a alter in protein production can sometimes be beneficial
  20. 20. © 2014 Pearson Education, Inc. Altering Gene Number or Position  Chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful  Duplication of minor pieces of Dna increases genome size and is ordinarily less harmful  Duplicated genes can take on new functions by farther mutation  An bequeathed odor-detecting cistron has been duplicated many times: Humans have 350 functional copies of the factor; mice have i,000
  21. 21. © 2014 Pearson Education, Inc. Rapid Reproduction  Mutation rates are low in animals and plants  The average is about i mutation in every 100,000 genes per generation  Mutation rates are often lower in prokaryotes and higher in viruses  Brusque generation times allow mutations to accrue rapidly in prokaryotes and viruses
  22. 22. © 2014 Pearson Instruction, Inc. Sexual Reproduction  In organisms that reproduce sexually, virtually genetic variation results from recombination of alleles  Sexual reproduction can shuffle existing alleles into new combinations through three mechanisms: crossing over, independent array, and fertilization
  23. 23. © 2014 Pearson Education, Inc. Concept 21.two: The Hardy-Weinberg equation can be used to test whether a population is evolving  The showtime pace in testing whether evolution is occurring in a population is to analyze what we mean by a population
  24. 24. © 2014 Pearson Education, Inc. Gene Pools and Allele Frequencies  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  An allele for a particular locus is fixed if all individuals in a population are homozygous for the aforementioned allele
  25. 25. © 2014 Pearson Pedagogy, Inc. Effigy 21.6 Porcupine herd Beaufort Sea Fortymile herd Porcupine herd range Fortymile herd range MAP Expanse ALASKA CANADA NORTHWEST TERRITORIES YUKON ALASKA
  26. 26. © 2014 Pearson Education, Inc. Figure 21.6a Porcupine herd
  27. 27. © 2014 Pearson Didactics, Inc. Figure 21.6b Fortymile herd
  28. 28. © 2014 Pearson Education, Inc.  The frequency of an allele in a population can be calculated  For diploid organisms, the total number of alleles at a locus is the full number of individuals times 2  The full number of dominant alleles at a locus is 2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous private; the aforementioned logic applies for recessive alleles
  29. 29. © 2014 Pearson Education, Inc.  Past convention, if there are 2 alleles at a locus, p and q are used to represent their frequencies  The frequency of all alleles in a population will add together up to one  For example, p + q = 1
  30. 30. © 2014 Pearson Education, Inc. Figure 21.UN01 CR CR CR CW CW CW
  31. 31. © 2014 Pearson Education, Inc.  For example, consider a population of wildflowers that is incompletely dominant for color  320 ruby-red flowers (CR CR )  160 pinkish flowers (CR CW )  20 white flowers (CW CW )  Summate the number of copies of each allele  CR = (320 × 2) + 160 = 800  CW = (xx × 2) + 160 = 200
  32. 32. © 2014 Pearson Didactics, Inc.  To calculate the frequency of each allele  p = freq CR = 800 / (800 + 200) = 0.8 (80%)  q = 1 − p = 0.2 (20%)  The sum of alleles is always i  0.8 + 0.ii = 1
  33. 33. © 2014 Pearson Education, Inc. The Hardy-Weinberg Principle  The Hardy-Weinberg principle describes a population that is non evolving  If a population does non meet the criteria of the Hardy-Weinberg principle, it can exist concluded that the population is evolving
  34. 34. © 2014 Pearson Education, Inc.  The Hardy-Weinberg principle states that frequencies of alleles and genotypes in a population remain constant from generation to generation  In a given population where gametes contribute to the adjacent generation randomly, allele frequencies will not change  Mendelian inheritance preserves genetic variation in a population Hardy-Weinberg Equilibrium
  35. 35. © 2014 Pearson Pedagogy, Inc.  Hardy-Weinberg equilibrium describes the constant frequency of alleles in such a gene puddle  Consider, for example, the aforementioned population of 500 wildflowers and 1,000 alleles where  p = freq CR = 0.8  q = freq CW = 0.2
  36. 36. © 2014 Pearson Education, Inc. Figure 21.7 Frequencies of alleles Gametes produced p = frequency of CR allele q = frequency of CW allele Alleles in the population Each egg: Each sperm: = 0.8 = 0.2 80% chance 80% chance 20% chance xx% take a chance
  37. 37. © 2014 Pearson Education, Inc.  The frequency of genotypes can be calculated  CR CR = p2 = (0.eight)2 = 0.64  CR CW = 2pq = 2(0.8)(0.two)= 0.32  CW CW = q2 = (0.2)two = 0.04  The frequency of genotypes tin can be confirmed using a Punnett square
  38. 38. © 2014 Pearson Pedagogy, Inc. Effigy 21.viii Sperm Eggs 80% CR (p = 0.8) 20% CW (q = 0.2) p = 0.viii q = 0.2CR CR CW CW p = 0.eight q = 0.2 0.64 (p2 ) CR CR 0.16 (pq) CR CW 0.16 (qp) CR CW 0.04 (q2 ) CW CW Gametes of this generation: 64% CR CR , 32% CR CW , and 4% CW CW 64% CR (from CR CR plants) 16% CR (from CR CW plants) iv% CW (from CW CW plants) 16% CW (from CR CW plants) 80% CR = 0.viii = p 20% CW = 0.2 = q + + = = 64% CR CR , 32% CR CW , and four% CW CW plants With random mating, these gametes will result in the same mix of genotypes in the adjacent generation:
  39. 39. © 2014 Pearson Education, Inc. Effigy 21.8a Sperm Eggs fourscore% CR (p = 0.eight) 20% CW (q = 0.two) p = 0.8 q = 0.2CR CR CW CW p = 0.viii q = 0.2 0.64 (p2 ) CR CR 0.16 (pq) CR CW 0.16 (qp) CR CW 0.04 (q2 ) CW CW
  40. 40. © 2014 Pearson Education, Inc. Effigy 21.8b Gametes of this generation: 64% CR CR , 32% CR CW , and 4% CW CW 64% CR (from CR CR plants) sixteen% CR (from CR CW plants) iv% CW (from CW CW plants) 16% CW (from CR CW plants) eighty% CR = 0.8 = p twenty% CW = 0.2 = q + + = = 64% CR CR , 32% CR CW , and 4% CW CW plants With random mating, these gametes will result in the aforementioned mix of genotypes in the next generation:
  41. 41. © 2014 Pearson Education, Inc.  If p and q stand for the relative frequencies of the only two possible alleles in a population at a detail locus, then  p2 + 2pq + q2 = 1 where p2 and q2 stand for the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype
  42. 42. © 2014 Pearson Education, Inc. Figure 21.UN02
  43. 43. © 2014 Pearson Education, Inc. Conditions for Hardy-Weinberg Equilibrium  The Hardy-Weinberg theorem describes a hypothetical population that is non evolving  In existent populations, allele and genotype frequencies exercise change over time
  44. 44. © 2014 Pearson Instruction, Inc.  The five conditions for nonevolving populations are rarely met in nature 1. No mutations 2. Random mating 3. No natural selection 4. Extremely big population size 5. No gene menstruum
  45. 45. © 2014 Pearson Education, Inc.  Natural populations can evolve at some loci while being in Hardy-Weinberg equilibrium at other loci  Some populations evolve slowly enough that evolution cannot be detected
  46. 46. © 2014 Pearson Instruction, Inc. Applying the Hardy-Weinberg Principle  We can assume the locus that causes phenylketonuria (PKU) is in Hardy-Weinberg equilibrium given that 1. The PKU factor mutation rate is low 2. Mate pick is random with respect to whether or not an individual is a carrier for the PKU allele
  47. 47. © 2014 Pearson Pedagogy, Inc. iii. Natural selection can simply human activity on rare homozygous individuals who do not follow dietary restrictions iv. The population is large 5. Migration has no consequence, as many other populations have like allele frequencies
  48. 48. © 2014 Pearson Education, Inc.  The occurrence of PKU is one per ten,000 births  q2 = 0.0001  q = 0.01  The frequency of normal alleles is  p = 1 – q = 1 – 0.01 = 0.99  The frequency of carriers is  2pq = 2 × 0.99 × 0.01 = 0.0198  or approximately 2% of the U.Due south. population
  49. 49. © 2014 Pearson Educational activity, Inc.  3 major factors alter allele frequencies and bring about most evolutionary change  Natural selection  Genetic migrate  Cistron menses Concept 21.three: Natural selection, genetic drift, and gene flow tin alter allele frequencies in a population
  50. 50. © 2014 Pearson Pedagogy, Inc. Natural Option  Differential success in reproduction results in sure alleles existence passed to the next generation in greater proportions  For example, an allele that confers resistance to Ddt increased in frequency afterward Ddt was used widely in agronomics
  51. 51. © 2014 Pearson Education, Inc. Genetic Migrate  The smaller a sample, the more likely it is that chance lone will cause deviation from a predicted consequence  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, particularly in small populations Animation: Causes of Evolutionary Changes Animation: Mechanisms of Evolution
  52. 52. © 2014 Pearson Education, Inc. Figure 21.9-1 CW CW CR CR CR CW CR CR CR CR CR CR CR CR CR CW CR CW CR CW p (frequency of CR ) = 0.7 q (frequency of CW ) = 0.3 Generation 1
  53. 53. © 2014 Pearson Education, Inc. Effigy 21.9-2 CW CW CR CR CR CW CR CR CR CR CR CR CR CR CR CW CR CW CR CW CW CW CR CR CR CW CR CR CR CR CR CW CR CW CR CW CW CW CW CW 5 plants leave offspring p (frequency of CR ) = 0.7 q (frequency of CW ) = 0.three p = 0.5 q = 0.v Generation 2Generation 1
  54. 54. © 2014 Pearson Educational activity, Inc. Figure 21.9-3 CW CW CR CR CR CW CR CR CR CR CR CR CR CR CR CW CR CW CR CW CW CW CR CR CR CW CR CR CR CR CR CR CR CR CR CW CR CW CR CW CW CW CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR CW CW 5 plants exit offspring 2 plants get out offspring p (frequency of CR ) = 0.7 q (frequency of CW ) = 0.3 p = 0.5 q = 0.5 p = i.0 q = 0.0 Generation 2 Generation 3Generation i
  55. 55. © 2014 Pearson Didactics, Inc. The Founder Result  The founder effect occurs when a few individuals become isolated from a larger population  Allele frequencies in the small founder population tin be different from those in the larger parent population due to chance
  56. 56. © 2014 Pearson Education, Inc. The Bottleneck Effect  The clogging effect can result from a drastic reduction in population size due to a sudden environmental modify  Past risk, the resulting gene pool may no longer be reflective of the original population'due south gene puddle  If the population remains small-scale, it may be further afflicted by genetic migrate
  57. 57. © 2014 Pearson Education, Inc. Figure 21.10 Original population Surviving population Bottlenecking issue (a) By chance, bluish marbles are overrepresented in the surviving population. (b) Florida panther (Puma concolor coryi)
  58. 58. © 2014 Pearson Education, Inc. Effigy 21.10a-1 Original population (a) By hazard, blueish marbles are overrepresented in the surviving population.
  59. 59. © 2014 Pearson Educational activity, Inc. Effigy 21.10a-ii Original population Bottlenecking upshot (a) By gamble, blue marbles are overrepresented in the surviving population.
  60. 60. © 2014 Pearson Pedagogy, Inc. Figure 21.10a-3 Original population Surviving population Bottlenecking issue (a) By chance, bluish marbles are overrepresented in the surviving population.
  61. 61. © 2014 Pearson Didactics, Inc. Figure 21.10b (b) Florida panther (Puma concolor coryi)
  62. 62. © 2014 Pearson Didactics, Inc.  Understanding the clogging effect can increment understanding of how human action affects other species
  63. 63. © 2014 Pearson Education, Inc. Case Study: Touch of Genetic Drift on the Greater Prairie Chicken  Loss of prairie habitat acquired a severe reduction in the population of greater prairie chickens in Illinois  The surviving birds had depression levels of genetic variation, and only 50% of their eggs hatched
  64. 64. © 2014 Pearson Education, Inc. Effigy 21.eleven Pre-bottleneck (Illinois, 1820) Post-bottleneck (Illinois, 1993) Range of greater prairie chicken Illinois 1930–1960s 1993 Greater prairie chicken Kansas, 1998 (no bottleneck) Nebraska, 1998 (no clogging) 1,000–25,000 <l 75,000– 200,000 v.2 three.seven Location Population size 750,000 Number of alleles per locus Percentage of eggs hatched 93 <fifty 5.viii 5.8 99 96 (a) (b)
  65. 65. © 2014 Pearson Didactics, Inc. Figure 21.11a Pre-bottleneck (Illinois, 1820) Mail service-clogging (Illinois, 1993) Range of greater prairie chicken Greater prairie chicken (a)
  66. 66. © 2014 Pearson Education, Inc. Figure 21.11b Illinois 1930–1960s 1993 Kansas, 1998 (no bottleneck) Nebraska, 1998 (no bottleneck) i,000–25,000 <50 75,000– 200,000 5.2 iii.7 Location Population size 750,000 Number of alleles per locus Percentage of eggs hatched 93 <50 5.8 5.8 99 96 (b)
  67. 67. © 2014 Pearson Instruction, Inc. Figure 21.11c Greater prairie chicken
  68. 68. © 2014 Pearson Pedagogy, Inc.  Researchers used DNA from museum specimens to compare genetic variation in the population before and after the bottleneck  The results showed a loss of alleles at several loci  Researchers introduced greater prairie chickens from populations in other states and were successful in introducing new alleles and increasing the egg hatch rate to 90%
  69. 69. © 2014 Pearson Education, Inc. Effects of Genetic Drift: A Summary 1. Genetic drift is meaning in small populations ii. Genetic drift tin can crusade allele frequencies to change at random 3. Genetic drift can lead to a loss of genetic variation within populations four. Genetic migrate can cause harmful alleles to go stock-still
  70. seventy. © 2014 Pearson Education, Inc. Cistron Menstruation  Gene catamenia consists of the movement of alleles among populations  Alleles can be transferred through the motion of fertile individuals or gametes (for instance, pollen)  Gene flow tends to reduce genetic variation among populations over time
  71. 71. © 2014 Pearson Pedagogy, Inc.  Factor flow can subtract the fitness of a population  Consider, for example, the great tit (Parus major) on the Dutch island of Vlieland  Immigration of birds from the mainland introduces alleles that decrease fitness in island populations  Natural option reduces the frequency of these alleles in the eastern population where immigration from the mainland is depression  In the central population, high clearing from the mainland overwhelms the furnishings of choice
  72. 72. © 2014 Pearson Teaching, Inc. Figure 21.12 Survivalrate(%) Central population Vlieland, kingdom of the netherlands Eastern population NORTH Ocean 2 km Population in which the surviving females eventually bred Females born in central population Parus major Primal Eastern Females born in eastern population threescore 50 40 30 20 10 0
  73. 73. © 2014 Pearson Pedagogy, Inc. Figure 21.12a Survivalrate(%) Population in which the surviving females eventually bred Females born in central population Cardinal Eastern Females born in eastern population 60 l 40 thirty 20 x 0
  74. 74. © 2014 Pearson Didactics, Inc. Figure 21.12b Parus major
  75. 75. © 2014 Pearson Instruction, Inc.  Gene flow can increase the fitness of a population  Consider, for instance, the spread of alleles for resistance to insecticides  Insecticides take been used to target mosquitoes that carry Due west Nile virus and other diseases  Alleles have evolved in some populations that confer insecticide resistance to these mosquitoes  The flow of insecticide resistance alleles into a population can cause an increase in fitness
  76. 76. © 2014 Pearson Didactics, Inc.  Gene flow is an important agent of evolutionary change in modern human populations
  77. 77. © 2014 Pearson Teaching, Inc.  Evolution past natural option involves both chance and "sorting"  New genetic variations arise by chance  Beneficial alleles are "sorted" and favored by natural selection  Just natural selection consistently results in adaptive evolution, an increment in the frequency of alleles that improve fitness Concept 21.4: Natural choice is the simply mechanism that consistently causes adaptive evolution
  78. 78. © 2014 Pearson Education, Inc. Natural Selection: A Closer Wait  Natural selection brings well-nigh adaptive development by acting on an organism's phenotype
  79. 79. © 2014 Pearson Didactics, Inc. Relative Fettle  The phrases "struggle for existence" and "survival of the fittest" are misleading as they imply direct competition amidst individuals  Reproductive success is generally more than subtle and depends on many factors
  80. 80. © 2014 Pearson Education, Inc.  Relative fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals  Selection indirectly favors certain genotypes by acting straight on phenotypes
  81. 81. © 2014 Pearson Instruction, Inc. Directional, Confusing, and Stabilizing Selection  At that place are iii modes of natural selection  Directional choice favors individuals at one end of the phenotypic range  Disruptive choice favors individuals at both extremes of the phenotypic range  Stabilizing selection favors intermediate variants and acts confronting extreme phenotypes
  82. 82. © 2014 Pearson Education, Inc. Effigy 21.13 Original population Evolved population Original population Frequencyof individuals Phenotypes (fur colour) (a) Directional selection (b) Disruptive selection (c) Stabilizing selection
  83. 83. © 2014 Pearson Didactics, Inc. The Key Office of Natural Selection in Adaptive Evolution  Striking adaptations accept arisen by natural option  For example, sure octopuses can change color rapidly for cover-up  For example, the jaws of snakes permit them to swallow prey larger than their heads
  84. 84. © 2014 Pearson Pedagogy, Inc. Figure 21.14 Bones shown in green are movable. Ligament
  85. 85. © 2014 Pearson Education, Inc. Figure 21.14a
  86. 86. © 2014 Pearson Teaching, Inc.  Natural pick increases the frequencies of alleles that raise survival and reproduction  Adaptive evolution occurs as the match between an organism and its surroundings increases  Because the surroundings tin alter, adaptive evolution is a continuous, dynamic procedure
  87. 87. © 2014 Pearson Education, Inc.  Genetic drift and gene flow do not consistently lead to adaptive evolution, as they can increase or decrease the match between an organism and its environment
  88. 88. © 2014 Pearson Education, Inc. Sexual Option  Sexual selection is natural selection for mating success  It can event in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics
  89. 89. © 2014 Pearson Pedagogy, Inc. Figure 21.fifteen
  90. 90. © 2014 Pearson Education, Inc.  Intrasexual selection is competition amongst individuals of one sex (often males) for mates of the reverse sex  Intersexual selection, often chosen mate selection, occurs when individuals of 1 sex (usually females) are finicky in selecting their mates  Male showiness due to mate option can increase a male's chances of attracting a female, while decreasing his chances of survival
  91. 91. © 2014 Pearson Education, Inc.  How do female preferences evolve?  The "adept genes" hypothesis suggests that if a trait is related to male person genetic quality or health, both the male trait and female preference for that trait should increase in frequency
  92. 92. © 2014 Pearson Didactics, Inc. Figure 21.16 SC male grayness tree frog LC male grayness tree frog Female gray tree frog Recording of SC male person'south telephone call Recording of LC male'south call Offspring of SC begetter SC sperm × Eggs × LC sperm Offspring of LC begetter Survival and growth of these half-sibling offspring compared Experiment Results
  93. 93. © 2014 Pearson Didactics, Inc. Figure 21.16a SC male person gray tree frog LC male gray tree frog Female gray tree frog Recording of SC male'southward phone call Recording of LC male person's call Offspring of SC begetter SC sperm × Eggs × LC sperm Offspring of LC father Survival and growth of these one-half-sibling offspring compared Experiment
  94. 94. © 2014 Pearson Educational activity, Inc. Figure 21.16b Results
  95. 95. © 2014 Pearson Education, Inc. The Preservation of Genetic Variation  Neutral variation is genetic variation that does non confer a selective advantage or disadvantage  Various mechanisms help to preserve genetic variation in a population
  96. 96. © 2014 Pearson Education, Inc. Diploidy  Diploidy maintains genetic variation in the class of subconscious recessive alleles  Heterozygotes can deport recessive alleles that are hidden from the effects of pick
  97. 97. © 2014 Pearson Pedagogy, Inc. Balancing Selection  Balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population  Balancing selection includes  Heterozygote advantage  Frequency-dependent selection
  98. 98. © 2014 Pearson Didactics, Inc.  Heterozygote reward occurs when heterozygotes have a college fitness than do both homozygotes  Natural selection will tend to maintain ii or more alleles at that locus  For example, the sickle-cell allele causes deleterious mutations in hemoglobin but as well confers malaria resistance
  99. 99. © 2014 Pearson Education, Inc. Figure 21.17 Distribution of malaria caused by Plasmodium falciparum (a parasitic unicellular eukaryote) Fundamental Frequencies of the sickle-jail cell allele ten.0–12.5% >12.five% 7.v–10.0% five.0–7.5% 2.5–5.0% 0–2.5%
  100. 100. © 2014 Pearson Education, Inc.  Frequency-dependent selection occurs when the fitness of a phenotype declines if it becomes besides common in the population  Selection can favor whichever phenotype is less common in a population  For example, frequency-dependent selection selects for approximately equal numbers of "right-mouthed" and "left-mouthed" scale-eating fish
  101. 101. © 2014 Pearson Didactics, Inc. Figure 21.18 "Left-mouthed" P. microlepis "Right-mouthed" P. microlepis Sample yr Frequencyof "left-mouthed"individuals 1981 '83 '85 '87 '89 0.5 0 i.0
  102. 102. © 2014 Pearson Instruction, Inc. Why Natural Pick Cannot Style Perfect Organisms 1. Choice can human action simply on existing variations 2. Evolution is limited past historical constraints 3. Adaptations are often compromises 4. Risk, natural selection, and the surround interact
  103. 103. © 2014 Pearson Educational activity, Inc. Effigy 21.xix
  104. 104. © 2014 Pearson Education, Inc. Figure 21.UN03
  105. 105. © 2014 Pearson Education, Inc. Figure 21.UN04 Original population Evolved population Directional selection Confusing selection Stabilizing choice
  106. 106. © 2014 Pearson Education, Inc. Figure 21.UN05 Salinity increases toward the open ocean Long Island Sound Atlantic Body of water Sampling sites (one–8 represent pairs of sites) Allele frequencies Other lap alleleslap94 alleles Data from R. Thousand. Koehn and T. J. Hilbish, The adaptive importance of genetic variation, American Scientist 75:134–141 (1987). Due north

  • Figure 21.ane Is this finch evolving?
  • Figure 21.2 Evidence of option by food source
  • Figure 21.three Phenotypic variation in horses
  • Figure 21.4 Extensive genetic variation at the molecular level
  • Figure 21.five Nonheritable variation
  • Figure 21.5a Nonheritable variation (part 1: oak flower diet)
  • Figure 21.5b Nonheritable variation (part 2: oak leaf diet)
  • Figure 21.half-dozen One species, two populations
  • Figure 21.6a One species, two populations (part i: porcupine herd)
  • Figure 21.6b One species, ii populations (part two: fortymile herd)
  • Effigy 21.UN01 In-text figure, incomplete authorisation, p. 403
  • Figure 21.seven Selecting alleles at random from a factor pool
  • Figure 21.8 The Hardy-Weinberg principle
  • Figure 21.8a The Hardy-Weinberg principle (part ane: Punnett square)
  • Figure 21.8b The Hardy-Weinberg principle (part ii: equations)
  • Effigy 21.UN02 In-text effigy, Hardy-Weinberg equation, p. 405
  • Effigy 21.9-1 Genetic drift (step i)
  • Figure 21.9-2 Genetic drift (pace 2)
  • Effigy 21.9-iii Genetic drift (step 3)
  • Figure 21.10 The bottleneck effect
  • Effigy 21.10a-1 The bottleneck upshot (part 1, step 1)
  • Figure 21.10a-2 The bottleneck effect (part 1, pace ii)
  • Figure 21.10a-3 The bottleneck consequence (part 1, step 3)
  • Figure 21.10b The bottleneck effect (part 2: photo)
  • Effigy 21.11 Genetic drift and loss of genetic variation
  • Figure 21.11a Genetic drift and loss of genetic variation (role 1: map)
  • Figure 21.11b Genetic drift and loss of genetic variation (function ii: table)
  • Figure 21.11c Genetic migrate and loss of genetic variation (role 3: photo)
  • Effigy 21.12 Gene catamenia and local adaptation
  • Figure 21.12a Factor flow and local adaptation (function ane: graph)
  • Figure 21.12b Gene flow and local adaptation (part 2: photo)
  • Figure 21.13 Modes of option
  • Figure 21.14 Movable jaw bones in snakes
  • Figure 21.14a Movable jaw bones in snakes (photograph)
  • Figure 21.xv Sexual dimorphism and sexual selection
  • Figure 21.16 Inquiry: Do females select mates based on traits indicative of "good genes"?
  • Figure 21.16a Inquiry: Practice females select mates based on traits indicative of "practiced genes"? (part one: experiment)
  • Figure 21.16b Inquiry: Do females select mates based on traits indicative of "good genes"? (part 2: results)
  • Figure 21.17 Mapping malaria and the sickle-cell allele
  • Effigy 21.xviii Frequency-dependent selection
  • Figure 21.nineteen Evolutionary compromise
  • Figure 21.UN03 Skills do: using the Hardy-Weinberg equation to translate information and make predictions
  • Figure 21.UN04 Summary of key concepts: modes of selection
  • Figure 21.UN05 Test your understanding, question seven (saltwater balance)

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