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Today

Today. Read over the Wallace article Leave on your table Quiz will start in 5 minutes Schedule Quiz Finish natural selection labs Ch. 23 notes Begin population genetics. After the quiz. Complete the analysis questions of the strawfish lab. Announcement.

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Today

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  1. Today • Read over the Wallace article • Leave on your table • Quiz will start in 5 minutes • Schedule • Quiz • Finish natural selection labs • Ch. 23 notes • Begin population genetics

  2. After the quiz • Complete the analysis questions of the strawfish lab

  3. Announcement • AP Test sign-ups have started (2/11 – 3/7) • $89 (financial aid available – talk to Ms. Clarke in the counseling office) • 12-15 hours of tuition at a state university is around $5000 • If you get credit for 3 hours, you would be saving $1000

  4. Lecture #10 • Chapter 23~ The Evolution of Populations

  5. Today • Mechanisms of genetic change within populations • Cause of variation • Altering allelic frequencies • Natural selection in depth • Preservation of genetic variation - necessary

  6. Microevolution – the change in the gene frequencies of a population over time

  7. 3 main causes of allelic changes • Gene flow – random, may not be beneficial, reduces differences between populations • Genetic Drift – random, may not be beneficial • Natural selection – interacts with environment, creates organisms that better interact with their environment (adaptive evolution)

  8. Variation within a population (Genetics review) • Discrete characters – usually determined by a single gene locus (either/or basis) • Purple or white flowers of pea plants • Quantitative characters – coded for by 2 or more genes (polygenic) • Height

  9. Biotechnology Review • Ways to measure average heterozygosity • Gel electrophoresis • 14% in fruit flies • Ways to measure nucleotide variability • PCR • Restriction fragment analysis (southern blotting) • .4% in humans

  10. Variation between populations • Geographic variation – same species organisms living in different environments exhibit genetic variation • Cline – a graded change in genetic variation and geography • Populations living on a slope of a mountain • Populations living at varying depths in the ocean

  11. Variation • Mutation – ultimate source of all variation • Point mutations – substitutions, frameshifts, chromosomal mutations (see diagram) • HIV • 1010 new viruses/day • RNA – higher mutation rate • Mutations in every gene each day • Drug cocktails • Reinfections • Animals • 1 mutation in every 100,000 genes

  12. Microevolution, VI • Mutations: a change in an organism’s DNA (gametes; many generations); original source of genetic variation (raw material for naturalselection) • Can be reversible • Most not beneficial • It does not change populations, genetic drift, gene flow, and natural selection do

  13. Transposons/transposable elements

  14. Gene Duplication

  15. Sexual Recombination • Gene shuffling during meiosis • Crossing over • Independent assortment • Random fertilization

  16. Population genetics • Population: a localized group of individuals belonging to the same species • Species: a group of populations whose individuals have the potential to interbreed and produce fertile offspring • Gene pool: the total aggregate of genes in a population at any one time • Population genetics: the study of genetic changes in populations • “Individuals (and their phenotypes) are selected, but populations evolve.”

  17. Hardy-Weinberg Theorem • Serves as a model for the genetic structure of a non-evolving population (equilibrium) • States that both allele and genotype frequencies in a population remain constant—that is, they are in equilibrium—from generation to generation unless specific disturbing influences are introduced. • 5 conditions: • 1- Very large population size; • 2- No migration; • 3- No net mutations; • 4- Random mating; • 5- No natural selection

  18. Hardy-Weinberg Equation • p=frequency of one allele (A); q=frequency of the other allele (a); p+q=1.0(p=1-q & q=1-p) • P2=frequency of AA genotype; 2pq=frequency of Aa plus aA genotype; q2=frequency of aa genotype; p2 + 2pq + q2 = 1.0

  19. Hardy-Weinberg Equation p + q = 1 p2 + 2pq + q2 = 1 • p = frequency of “A” allele and q = frequency of “a” allele • p2 = expected freq. of homozygotes for one allele (AA) • 2pq = expected freq. of heterozygotes (Aa) • q2 = expected freq. of homozygotes for the other allele (aa)

  20. Let’s Practice • 2 equations: • p + q = 1 • p2 + 2pq + q2 = 1 • Let’s say there are 2 types of teddy grahams, happy and sad • The happy bear is recessive • If 5 of 20 bears are happy, calculated p, q, p2, 2pq, and q2

  21. Happy Sad

  22. Steps of H-W problem • Calculate q2 – 5/20 = .25 • Calculate q – square root of .25 = .5 • Calculate p – (p + q = 1) = .5 • Calculate 2pq – 2 x .5 x .5 = .5 • Calculate p2 - .5 squared = .25

  23. What this means • In this gene pool, 50% of all the alleles are dominant and 50% are recessive • 25% of the population has the recessive phenotype • 75% of the population has the dominant phenotype (25% are homozygous dominant and 50% are heterozygous dominant)

  24. Practice

  25. 3 main causes of allelic changes • Gene flow – random, may not be beneficial, reduces differences between populations • Genetic Drift – random, may not be beneficial • Natural selection – interacts with environment, creates organisms that better interact with their environment (adaptive evolution)

  26. Microevolution, I • A change in the gene pool of a population over a succession of generations • Genetic drift: changes in the gene pool of a small population due to chance (usually reduces genetic variability)

  27. Microevolution, II • Founder Effect:a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population (island populations) • Inherited diseases

  28. Microevolution, III • The Bottleneck Effect: type of genetic drift resulting from a reduction in population (natural disaster) such that the surviving population is no longer genetically representative of the original population

  29. Microevolution, V • Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

  30. Microevolution, IV • Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment

  31. Today • Have out ch. 23 Notes (we are on # 24) • Ch. 23 and 24 Quiz – Friday • Test - Tuesday

  32. Let’s Focus on Natural selection • Fitness: contribution an individual makes to the gene pool of the next generation • It is a little more complicated than that (less fit genes can hitchhike with a fit gene) • Relative fitness: how an individual contributes to the next generation (sterile individuals have a relative fitness of 0) • Selection acts on phenotype directly and genotype indirectly

  33. Modes of natural selection 3 types: A. Directional B. Diversifying C. Stabilizing

  34. Natural Selection as Genetic Change A. Natural Selection has 3 affects on phenotype distribution • Directional Selection- Individuals on one end of a curve are “better fitted” than the middle or other end Peccaries naturally choose to consume those cactus plants with the fewest spinesAs a result, at flowering time there are more cacti with higher spine numbers; thus, there are more of their alleles going into pollen, eggs, and seeds for the next generation.

  35. Stabilizing Selection

  36. Natural Selection has 3 affects on phenotype distribution • Stabilizing Selection- Individuals near center of a curve are “better fitted” than both ends Peccaries are consuming the low-spine number plants, and the insects are killing the high-spine-number plants. As these gene combinations are removed from the cactus gene pool, there is less and less variety possible in subsequent generations.

  37. (DIVERSIFYING)

  38. Natural Selection has 3 affects on phenotype distribution • Disruptive Selection- Individuals at upper and lower ends are “better fitted” the ones in the middle Years of collecting have left their toll on the roadside cacti. In this environment, it is maladaptive to be good looking and have a reasonable number of spines. Low spine-number plants are not picked because they don't "look right", and high spine-number varieties are left alone because they are too hard to pick. Gradually, the gene pool changes in favor of the two extreme spine number types.

  39. Sexual selection • Creates Sexual dimorphism: secondary sex characteristic distinction • Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism • Intrasexual – males competing (alpha male) • Intersexual – females choosing

  40. Variation preservation • Prevention of natural selection’s reduction of variation • 1. Diploidy 2nd set of chromosomes hides variation in the heterozygote • 2. Balanced polymorphism -heterozygote advantage (hybrid vigor; i.e., malaria/sickle-cell anemia); -frequency dependent selection (survival & reproduction of any 1 morph declines if it becomes too common; i.e., parasite/host)

  41. 4 reasons natural selection does not produce perfect organims • Selection can only act on existing variations - New alleles do not arise on demand • Evolution is limited by historical constraints -Each species has a legacy • Adaptations are often compromises - Structural reinforcement vs. agility • Chance, natural selection, and the environment interact -Hurricanes, environments changing year to year

  42. Population variation • Polymorphism:coexistence of 2 or more distinct forms of individuals (morphs) within the same population • Geographical variation:differences in genetic structure between populations due to environment (cline)

  43. Natural Selection Labs • Finish the “Strawfish lab” questions • I will assign each table with a specific scenario to whiteboard and explain to the class • Things to include on whiteboard: • Graph • Data table of allelic frequencies (initial and final only) • Be ready to explain the following: • What was the premise of the “trial” • What results you got • Why the results happened

  44. Population Genetics Lab

  45. Microevolution, VII • 4- Nonrandom mating (selective breeding): inbreeding and assortive mating (both shift frequencies of different genotypes)

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