Mead AP Biology LAP 6 Population Genetics and Evolution Chapters 22-24 22.1 Challenge to Traditional Views: Historical Context for Darwin A. Resistance to Idea of Evolution ◦ Scale of Nature Plato Aristotle ◦ Judeo-Christian Natural Theology Linnaeus ◦ Catastrophism Cuvier studies fossils Paris basin Extinction NOT due to evolution B. Gradualism ◦ Hutton ◦ Lyell- Uniformitarianism ◦ Fig. 22.2 Timeline C. Lamarck ◦ Use and Disuse theory, 1809 ◦ Inheritance of acquired characteristics ◦ Some good points ◦ Mechanism not correct 22.2 Darwinian Revolution A. Darwin’s Research ◦ Voyage of HMS Beagle 1831 Fig 22.5 ◦ Focus on Adaptation Return 1836 Connect adaptation to origin of new species Geographical barriers lead to divergence Finches, Fig 22.6 ◦ Alfred Russel Wallace Same ideas as Darwin Sent to Darwin for review in 1858 Presented by Lyell and Wallace Darwin published later in 1859 B. Origin of Species ◦ Descent with Modification, Fig 22.7 Occurrence of evolution Unity of life Common Ancestor ◦ Natural Selection and Adaptation Mechanism of evolution 3 key components 1. Differential reproductive success Malthus Doctrine of Human Suffering Over-reproduction ◦ ◦ Struggle for existence based on limited resources 2. Interaction of environment and existing variability 3. Product is adaptation to environment Evidence from artificial selection Fig 22.10 Wild mustard Cabbage Dramatic results in short time Natural selection should be able to do in hundreds or thousands of generations Points to remember Individuals don’t evolve, populations evolve Can only amplify or diminish heritable variations that already exist Traits favored by natural selection are situational Vary by time or place 22. 3 Darwin’s Theory Explains Wide Range of Observations A. Natural Selection in Action ◦ Differential predation and guppy population Fig 22.12 ◦ Evolution of drug-resistant HIV Fig 22.13 B. Homology ◦ Def ◦ Anatomical homology Homologous structures, Fig 22.14 Comparative embryology, Fig 22.15 Vestigial structures ◦ Molecular Homology, Fig 22.16 C. Biogeography ◦ Def ◦ Fig 22.17 D. Fossil Record ◦ Transitional forms ◦ Fig 22.18 23.1 Population Genetics A. Modern Synthesis ◦ Joining of Darwin and Mendel’s work ◦ Population genetics ◦ Gradualism ◦ Modern synthesis B. Genetic Structure of Populations ◦ Population Def Geographic range, Fig 23.3 ◦ Gene pool Def Fixed allele ◦ Allele frequencies p and q Example: 500 plants 320 red, 160 pink, 20 white C. Hardy-Weinberg Theory: Non-evolving Populations ◦ Frequencies remain constant ◦ p + q = 1 (100%) Allele frequencies ◦ Homozygous dominant = p2 ◦ Heterozygous = pq + pq = 2pq ◦ Homozygous recessive = q2 ◦ Hardy-Weinberg Equation p2 + 2pq + q2 = 1 (100%) Genotype frequencies ◦ Use to calculate frequencies for alleles or genotypes for a gene pool ◦ Fig 23.5 ◦ Solving problems: 1 in 10,000 suffer from PKU which is a recessively inherited disorder. What is the allele frequency for the dominant and recessive allele? What is the frequency for carriers? Assume Hardy-Weinberg equilibrium. ◦ ◦ ◦ ◦ Conditions for Hardy-Weinberg Equilibrium Very large population Smaller populations subject to genetic drift No gene flow No movement of genes in or out of gene pool No new mutations No modifications to gene pool Random mating No choosing of mates based on any phenotype No natural selection No differential survival based on traits More sample problems: If the frequency for the A allele is 70%, what is the frequency of individuals that are heterozygous? If 16% of individuals are homozygous recessive for a trait what is the frquency of the dominant allele? 23.2 Mutation and Sexual Recombination Produce Variation A. Mutation ◦ In cell lines that produce gametes ◦ Point mutations: small vs large effect Alter protein function ◦ Chromosome mutations ◦ Effect depends on generation length B. Sexual recombination ◦ Occur every generation ◦ Most variation due to this 23.3 Altering Population’s Genetic Composition A. Deviations from Hardy-Weinberg ◦ Any can cause evolution ◦ Mutation effects are small ◦ Recombination shuffles but doesn’t change frequencies ◦ Nonrandom mating Changes genotype frequencies Doesn’t affect allele frequencies ◦ Other 3 are major causes of evolution B. Genetic Drift ◦ Def ◦ Fig 23.7 ◦ 2 types Bottleneck effect, Fig 23.8 Founder effect C. Gene Flow ◦ Def ◦ Reduces differences between populations 23.4 Natural Selection: Primary mechanism for adaptive evolution A. Genetic variation 1. Variation within population Discrete characters Quantitative characters Polymorphism Measuring genetic variation Average heterozygosity 2. Variation between populations Geographical variation Due to natural selection or genetic drift Cline Fig 23.11: Inquiry example B. Natural Selection: Closer look ◦ Evolutionary fitness ◦ Modes of selection, Fig 23.12 1. Directional selection 2. Stabilizing selection 3. Disruptive selection C. Preserving Variation ◦ Diploidy ◦ Balancing Selection Balanced Polymorphism Def Due to 3 causes 1. Heterozygote advantage 2. Patchy environment 3. Frequency dependent selection ◦ Neutral Variation D. Sexual selection ◦ Def ◦ Leads to sexual dimorphism Fig 23. 15 ◦ Intrasexual selection ◦ Intersexual selection E. Natural selection doesn’t make perfect organism ◦ Limited by historical constraints ◦ Adaptations are often compromises ◦ Chance and selection interact ◦ Selection only acts on variations that exist ◦ Operates on a “better than” basis 24.1 What is a Species? A. Biological Species Concept ◦ Def ◦ Occur in natural environment B. Reproductive Isolation ◦ Biological barriers ◦ Summarized in Fig 24.4 ◦ Pre-zygotic barriers Impede mating 1. Habitat isolation 2. Behavioral isolation 3. Temporal isolation Impede fertilization 1. Mechanical isolation 2. Gametic isolation ◦ Post-zygotic barriers Def Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown C. Limitations to biological species concept D. Other definitions of species ◦ Morphological species concept ◦ ◦ ◦ Paleontological species concept Ecological species concept Phylogenic species concept 24.2 Modes of Speciation A. Allopatric speciation ◦ Geographical barriers ◦ Fig 24.6 Example ◦ Conditions favoring allopatric speciation Small populations Fringe isolation: Splinter population or peripheral isolate Why good candidates B. Sympatric speciation ◦ Def ◦ Genetic change creates reproductive barrier ◦ Polyploidy in plants Def Fig 24. 8 Autoploidy ◦ Alloploidy Def More common form of polyploidy Hybrid usually sterile but can use asexual repro. Mutation may allow sex repro Fig 24.9 ◦ Animal sympatric speciation Polyploidy less common than in plants Utilize other mechanisms Reproductive isolation Differences in resource utilization Habitat differentiation Sexual selection Cichlids, Fig 24.10 C. Adaptive Radiation ◦ Def ◦ Example: Hawaii Fig 24.12 D. Tempo of Speciation ◦ Punctuated equilibrium ◦ Def, Fig 24.13 ◦ Fossil record ◦ Relative speed ◦ Debate ◦ Gradualism 24.3 Macroevolution is Combo of Many Speciation Events A. Evolutionary Novelties ◦ Improved versions of simpler structures ◦ Fig 24.14 B. Evolution of Genes that Control Dev’t ◦ ◦ Changes in rate and timing Heterochrony Allometric growth Fig 24.15 Fig 24. 16 Salamanders Heterochrony Fig 24. 17 Paedomorphosis Def Changes in spatial pattern Homeotic genes Hox genes Fig 24.18 and 24.19 Evolution is NOT goal oriented!