24.4 The nature of natural selection and adaptation Key concepts! Selection acts on individuals Evolution occurs at population level Evolution is NOT ?progressive? Not all traits adaptative Genetic constraints Fig 24.15 How do you explain the conceptual differences in these figures? Evolutionary Processes 14. (Campbell) Mendelian genetics 25.1 Analysis of allele frequency change: Hardy- Weinberg principle 25.2 Natural selection & sexual selection 25.3 Genetic Drift 25.4 Gene Flow 25.5 Mutation 25.6 Inbreeding Fig. 14-1 Fig. 14-3-3 EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers × F1 Generation (hybrids) All plants had purple flowers F2 Generation 705 purple-flowered plants 224 white-flowered plants Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers What Mendel Didn?t Know? Fig. 14-5-3 P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP P pp p F1 Generation Gametes: Genetic makeup: Appearance: Purple flowers Pp P p 1 /2 1 /2 F2 Generation Sperm Eggs P P PP Pp p p Pp pp 3 1 Fig. 14-15b 1st generation (grandparents) 2nd generation (parents, aunts, and uncles) 3rd generation (two sisters) Widow?s peak No widow?s peak (a) Is a widow?s peak a dominant or recessive trait? Ww ww Ww Wwww ww ww wwWw Ww wwWW Ww or Fig. 14-15c Attached earlobe 1st generation (grandparents) 2nd generation (parents, aunts, and uncles) 3rd generation (two sisters) Free earlobe (b) Is an attached earlobe a dominant or recessive trait? Ff Ff Ff Ff Ff ff Ff ff ff ff ff FF or or FF Ff Mendelian Genetics ? check on vocabulary What is a gene? What is an allele? What is a locus? What is a phenotype? Fig 25.2 Punnett square Fig 25.1 25.1 Analyzing change in allele frequencies: The Hardy-Weinberg Principle 4 major evolutionary mechanisms result in allele shifts: Natural selection Gene flow Genetic drift Mutation Hardy-Weinberg principle assumes no evolutionary mechanism is acting on the population AND random mating occurs Assume H-W equilibrium holds: The trait for 'male-pattern baldness' is a recessive trait encoded for by "b". Non-balding is encoded for by a dominant allele encoded for by the letter "B". A street survey conducted by Hair Club for Men found that out of 1000 men, 360 had male pattern baldness, the other 480 who did not and were heterozygous, and 160 who did not and were homozygous for a full head of hair. What is the frequency of the non-bald phenotype? What is the frequency of the bald allele? Chapter 25 Evolutionary Processes 25.1 Analysis of allele frequency change: Hardy-Weinberg principle 25.2 Natural selection & sexual selection 25.3 Genetic Drift 25.4 Gene Flow 25.5 Mutation 25.6 Inbreeding 25.2 Types of natural selection 1. Directional Selection 2. Stabilizing Selection 3. Disruptive Selection Fig 25.3 Directional Selection Fig 25.3 Fig 25.4 Stabilizing Selection Fig 25.4 Fig 25.5 Disruptive Selection Fig 25.5 Which type of selection? Non-Directional Selection 24.3 Genetic Drift Drosophila melanogaster example http://evolution.berkeley.edu/evolibrary/article/_0/evo_39 Founder effect Population bottleneck 24.4 Gene Flow 24.5 Mutation Genetic drift in small populations: Allele frequencies fluctuate unpredictably from one generation to the next Random (or Neutral) change that reduces genetic variation Campbell Figure 23.7 C R C R C R C W C R C R C W C W C R C R C R C W C R C W C R C W C R C R C R C R Only 5 of 10 plants leave offspring C W C W C R C R C R C W C R C R C W C W C R C W C W C W C R C R C R C W C R C W Only 2 of 10 plants leave offspring C R C R C R C R C R C R C R C R C R C R C R C R C R C R C R C R C R C R C R C R Generation 2 p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0 Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 Codominant: genotype = phenotype Fig 25.6 Genetic drift in small populations Fig 25.7 Genetic drift in small populations Genetic drift: Major evolutionary mechanism Genetic drift: change in allele frequency due to chance When is genetic drift likely to play a significant role? Bottleneck effects http://www.bergoiata.org/fe/felins/High %20Velocity,%20Cheetah.jpg Founder effect: island species Example: gene causing colorblindness http://serendip.brynmawr.edu/biology/b103/f01/web3/wise.html Non-random mating?inbreeding Fig 25.11 Example of inbreeding Sexual selection 1.female choice http://staff.washington.edu/andid/peacock-wooing-peahen.jpg Fig 25.12 Fig 25.12 Fig 25.14 Male-male competition Fig.25.14 Fig 25.15 Jennie Burger WELCOME TO BIOLOGY 2002
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