AP Bio: Wednesday, 4/4/12 Mini-Unit: MicroEvolution

1. AP Bio: Wednesday, 4/4/12Mini-Unit: MicroEvolution • Homework: Get started on PS 17. • Do Now: • Take out last night’s HW so you have it handy • What do you think is the difference between macroevolution and microevolution? • What does evolution have to do with genetics? • Today’s Goals: • Explain the difference between macro and microevolution • Apply the Hardy-Weinberg equations to analyzing gene pools in populations • Describe microevolutionary forces that cause changes in gene pools over time

2. EVOLUTION

3. Macroevolution – • One species can branch into two or more species • All life on earth is descended from common ancestors Microevolution – • Changes in the heritable characteristics in a population over time (population genetics)

4. Populations Genetics(Microevolution) Are populations evolving? How? Why?

5. Some definitions… • Species – • a group of organisms with similar characteristics and genetics that can reproduce and make fertile offspring • Population – • a group of organisms of the same species that live in a given area • Gene pool – • the collection of all the genes (and alleles) in a population • Allele frequency – • the proportion of one allele in the gene pool

6. Example: In cats, black hair is dominant over white hair. (B = black, b = white) Imagine a population of 500 cats: 320 are homozygous dominant 160 are heterozygous 20 are homozygous recessive • How many alleles are in the gene pool for this gene? • What is the frequency of the B allele?

7. Hardy-Weinberg Theoremof Genetic Equilibrium In a non-evolving population, frequencies of alleles and genotypes should remain constant across generations.

8. Hardy-Weinberg equations Allele frequencies: p = freq. A allele q = freq. a allele By definition: p + q = 1 Genotype frequencies: Freq. of AA genotype = Freq. of Aa genotype = Freq. of aa genotype = Prediction under HW equilibrium: p2 + 2pq + q2 = 1 p2 2pq pq + qp = q2

9. figure 21-07.jpg Use HW to do two things: Calculate allele frequencies (given genotype freq’s) Predict genotype frequencies (given allele freq’s)

10. Populations Genetics Are populations evolving? How? Why? H-W equations let us answer a specific aspect of this question: Are gene (allele) and/or genotype frequencies changing over time?

11. So what? If ACTUAL genotype frequencies match predictions, then… • the population is in HW equilibrium • allele and genotype freq. constant across generations (no evolution) If ACTUAL genotype frequencies differ from predictions, then… • population is not in HW equilibrium • some evolutionary force is acting!

12. Requirements for Hardy-Weinberg Equilibrium • No natural selection (due to limited resources, etc.) • No mutation • Random mating • No immigration or emigration (no gene flow) • Large population size

13. Evolutionary forces that violateHardy-Weinberg: • mutation • migration • non-random mating • genetic drift • selection How does each affect genetic variation within populations?

14. Mutation –transformation of one allele into another • generates genetic variation • alone, not a strong evolutionary force • provides the “raw material” of genetic variation on which selection and drift can act

15. Migration –movement of individuals between populations • “gene flow” between gene pools • maintains genetic variation within populations by bringing in new alleles • prevents populations from genetically diverging (and eventually becoming separate species)

16. Non-random mating • does not change allele freq’s • DOES change genotype freq’s Assortative mating – individuals prefer mates with same genotype increases homozygosity at a particular locus Disassortative – individuals prefer mates with different genotypes increases heterozygosity at a particular locus

17. Inbreeding –mating between close relatives • increases homozygosity across the genome • danger: “inbreeding depression” • inbred populations often show decreased fitness (due to greater risk of homozygous recessive disorders)

18. (Freeman & Herron 2001)

19. AP Bio: Thursday 4/5/12Hardy-Weinberg Problems & The Mating Game • Homework: Lab 8 Analysis Questions • Do Now: Do some math! • Imagine a population of 1,000 fruit flies: • 510 have gray bodies (wild-type, dominant) • 490 have black bodies (recessive) • What is the frequency of the recessive genotype? • What is the frequency of the recessive allele? • What is the frequency of the dominant allele? • How many flies would you predict to be… • Homozygous dominant? • Heterozygous?

20. Evolutionary forces that violateHardy-Weinberg: • mutation • migration • non-random mating • genetic drift • selection

21. Genetic drift –random changes in allele frequencies between generations • due to sampling error • greatest effect in small populations • population bottlenecks • founder effect

22. Genetic drift viapopulation bottleneck orfounder effect

23. Simulation:Genetic drift at one locus http://darwin.eeb.uconn.edu/simulations/drift.html

24. Selection –differential survival and reproduction of individuals with different genotypes • Non-random process (unlike genetic drift) • Natural selection involves… • More offspring are born than can survive • Competition/struggle for survival for limited resources • Variation between individuals that makes some better able to survive and reproduce • This variation is heritable/genetic (can be passed on) Result: Over many generations, the genotypes that are better able to survive and reproduce become more common in the population.

25. Simulation:Selection at one locus http://darwin.eeb.uconn.edu/simulations/selection.html

26. AP Bio: Thursday 4/5/12Hardy-Weinberg Problems & The Mating Game • Homework: Lab 8 Analysis Questions • Today’s Goals: • Use H-W equations to calculate allele and genotype frequencies • Explain how genetic drift and natural selection affect microevolution • Simulate population genetics and calculate allele and genotype frequencies in “The Mating Game”

27. AP Bio: Wednesday, 4/11/12Natural Selection & Sexual Selection • Homework: Due Friday: PS 17 and Lab 8 We will also have a short practice quiz on Friday – based on the problem set • Do Now: • Take out Lab 8 and turn to Part B • Get 2 sample papers and lick them. See if one tastes bad. • Today’s Goals: • Calculate allele and genotype frequencies for a REAL trait in our class (Part B) • Describe various effects of natural selection and sexual selection on the range of traits in a population.

28. Selection –differential survival and reproduction of individuals with different genotypes • Non-random process (unlike genetic drift) • Natural selection involves… • More offspring are born than can survive • Competition/struggle for survival for limited resources • Variation between individuals that makes some better able to survive and reproduce • This variation is heritable/genetic (can be passed on) Result: Over many generations, the genotypes that are better able to survive and reproduce become more common in the population.

30. Classify the following examples as Directional, Stabilizing, or Disruptive Selection: • Human birth weight tends to stay around 7 lbs. (too big = trouble for mom; too small = trouble for newborn) • Many seeds have seed coats of medium thickness (if too thin, no protection; if too thick, germinating seed can’t break through) • Finches need either small beaks (to eat tiny seeds) or large beaks (to crack large seeds).

31. Galapagos finches

33. Balanced Polymorphism(aka Heterozygote Advantage)Ex: sickle cell anemia

34. Frequency-dependent selection

35. Sexual Selection Peacock Experiments

36. Sexual Selection • Intrasexual – Members of one sex (usually male) compete for access to the other sex • Ex: Sea lions, rams • Intersexual – Members of one sex (usually female) choose certain members of the opposite sex over others • Ex: Pea hens choosing pea cocks