Chapter 21 Active Reading Guide: the Evolution of Populations
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- 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. © 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. © 2014 Pearson Instruction, Inc. Figure 21.ane
- 4. © 2014 Pearson Education, Inc. Figure 21.two 1978 (later drought) 10 1976 (like to the prior iii years) Averagebeakdepth(mm) ix 8 0
- 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
- 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
- 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. © 2014 Pearson Instruction, Inc. Figure 21.3
- 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. © 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. © 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. © 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. © 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. © 2014 Pearson Teaching, Inc. Figure 21.5a (a) Caterpillars raised on a nutrition of oak flowers
- 15. © 2014 Pearson Education, Inc. Figure 21.5b (b) Caterpillars raised on a diet of oak leaves
- sixteen. © 2014 Pearson Didactics, Inc. Sources of Genetic Variation New genes and alleles tin arise by mutation or gene duplication
- 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 2014 Pearson Education, Inc. Figure 21.6a Porcupine herd
- 27. © 2014 Pearson Didactics, Inc. Figure 21.6b Fortymile herd
- 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. © 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. © 2014 Pearson Education, Inc. Figure 21.UN01 CR CR CR CW CW CW
- 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 2014 Pearson Education, Inc. Figure 21.UN02
- 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 2014 Pearson Education, Inc. Effigy 21.10a-1 Original population (a) By hazard, blueish marbles are overrepresented in the surviving population.
- 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. © 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. © 2014 Pearson Didactics, Inc. Figure 21.10b (b) Florida panther (Puma concolor coryi)
- 62. © 2014 Pearson Didactics, Inc. Understanding the clogging effect can increment understanding of how human action affects other species
- 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. © 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. © 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. © 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. © 2014 Pearson Instruction, Inc. Figure 21.11c Greater prairie chicken
- 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. © 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
- 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. © 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. © 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. © 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. © 2014 Pearson Didactics, Inc. Figure 21.12b Parus major
- 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. © 2014 Pearson Didactics, Inc. Gene flow is an important agent of evolutionary change in modern human populations
- 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. © 2014 Pearson Education, Inc. Natural Selection: A Closer Wait Natural selection brings well-nigh adaptive development by acting on an organism's phenotype
- 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. © 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. © 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. © 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. © 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. © 2014 Pearson Pedagogy, Inc. Figure 21.14 Bones shown in green are movable. Ligament
- 85. © 2014 Pearson Education, Inc. Figure 21.14a
- 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. © 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. © 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. © 2014 Pearson Pedagogy, Inc. Figure 21.fifteen
- 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. © 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. © 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. © 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. © 2014 Pearson Educational activity, Inc. Figure 21.16b Results
- 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. © 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. © 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. © 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. © 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. © 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. © 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. © 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. © 2014 Pearson Educational activity, Inc. Effigy 21.xix
- 104. © 2014 Pearson Education, Inc. Figure 21.UN03
- 105. © 2014 Pearson Education, Inc. Figure 21.UN04 Original population Evolved population Directional selection Confusing selection Stabilizing choice
- 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
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