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EvolutionLab Lab Guide Week of January 25, 2010. Reading: LM 1; C:266-269
Updated: 1/18/10

EVOLUTION LAB 1 in custom lab manual Population Genetics I (Morgan/Dickey) plus demo of fossils, vertebrate embryos and vertebrate forelimbs to understand the evidence of evolution.

A. Review of Hardy-Weinberg Theorem and evidence for evolution (CONCEPTS from each section below: 10 min)

B. Exercise 1: model of Hardy-Weinberg Equilibrium using sampling with replacement (10 min).

C. Exercise 2A: Model Genetic drift and bottleneck; (20 min). DO NOT do founder effect.

D. Exercise 2C, Natural selection (30 min).

E. Experiment 2B: Gene flow (10 min).

F. NO COMPUTER SIMULATIONS;

G. Evidence for evolution. Students examine fossils, skeletons and embryos. (10 min)

H. Review (10 min)

I. Quiz (10 min)

1. A Population Genetics Simulations (From: Custom Lab Manual, 1-23)

   CONCEPTS: Hardy Weinberg Equilibrium (HWE) is a “null model” of no evolution within a population, i.e. allele frequencies remain constant through generations. Certain conditions must be met:

   a. population is very large

   b. no immigration or emigration

   c. no mutations

   d. mating is random

   e. no differential reproductive success

   Microevolution is any case breaking the rules of HWE

   Relevant lecture information: How populations evolve
   

   A. Review of Hardy-Weinberg Theorem and evidence for evolution (CONCEPTS, above: 10 min)

   B. Exercise 1: model of Hardy-Weinberg Equilibrium using sampling with replacement (10 min). Insructors must choose the bead color for the dominant allele. Students work in pairs. Instructors briefly explain, but do not do, Chi-Squared analysis . They only have to do this simulation through one generation to get the point that sexual recombination does not affect allele frequencies in the population.

   C. Exercise 2A: Model Genetic drift and bottleneck; (20 min). DO NOT do founder effect.

   • Bottleneck effect: for this, have students work as a bench (2 pairs combined), with one bag as the "active" bag, and the other as the reserve of beads. This gives them enough beads to have 50 individuals in their active bag, but a reserve of beads to adjust allele frequencies. Don't bother calculating p, q, 2pq for this.
   • Explain why sampling without replacement simulates a smaller population size.
   • After one generation, they will return the population to 50 individuals, but will adjust the allele frequency using their spare beads. As they finish (probably 5 generations), have them graph the allele frequency versus generation on the board,. Have every group use the same graph but results drawn in different colored chalk, so they can see the different results.
   • With any luck, their active bag will drift to one allele or the other so it will be ready for the natural selection exercise.

   D. Exercise 2C, Natural selection (30 min). Only do the industrial melanism simulation, as the sickle cell anemia simulation is a bit complex for non-majors.

   • Use the revised datasheet I have built; it is posted here. Have groups adjust their beads to make a population of 50 individuals that is 90% light alleles. They should store their other beads in one bag.
   • The only tricky point here compared to the other simulations is that, after determining the genotype frequencies for the new generation, they will need to subtract some due to “selection”, and THEN adjust the allele frequencies in their bags. This will take a little math, and it may be helpful to have a calculator on hand. Follow the simulation as described for 5-7 generations, and students will see obvious effects of selection.

   E. Experiment 2B: Gene flow (10 min). The same two groups that worked together for Experiment 2C will work together now; each bag is one population and, by the end of 2C, the bags should have very different allele frequencies.

   • Gene flow. Work as a bench again, but each pair has their own bag/population.
   • Instead of having them draw alleles, record, switch, etc. as the lab manual states, I find it is more effective to do it as a "magic trick." Just have students record the allele frequencies in each bag. Then each pair of students draw ten individuals from their bag, switch these to the other bag, and shake the bag to mix. Repeat 3 more times. Then recount the allele frequencies in each bag.
   • Most students seem a bit stunned that the ratio is almost 50:50 again by this point, so it sinks in that gene flow tends to normalize allele frequencies between two populations.
   • Ensure students do a final check that 50 beads of each color are in each bag; no quizzes until this is done!
   Required Equipment: A Population Genetics Simulations

   Type	#	Per	Item	Section	Notes
   E	1	Pair	Paper bag	A Population Genetics Simulations
   E	2	Pair	Dishes to contain beads	A Population Genetics Simulations
   E	1	Pair	100 beads: 50 each of 2 different colors	A Population Genetics Simulations

   So=Solution, S=Slide, Sp=Specimen, L=Living, E=Equipment

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2. B Macroevolution Demonstrations (From: Campbell et al. 2005, 260-263)

   Demonstrations of evidence for evolution, to support lectures 1 and 2. Students should be comfortable explaining how these data sets support the theory of evolution, using specific examples from the demos:

   1) Comparative morphology: homology of bones in the vertebrate forelimb

   Emphasize how the ancestral limb form has been modified for various tasks. Students are likely to only briefly look at specimens, so ensure they are taking the time to compare each limb to the ancestral state, region by region, using common terms (fingers, elbows). Also point out the skeletons on display in the hallway.

   2) Comparative embryology: similarity in embryonic form that differs from adult form

   Ensure students take the time to compare embryos and appreciate the common morphology. They must be able to identify the three major shared characters visible (pharyngeal slits, somites, post-anal tail)

   3) Fossil record: I want students to get an appreciation for the similarity between fossils and living organisms, and begin to have an idea of when various groups first appeared. Emphasize the fossils that are obviously like modern examples (teeth, shells).

   Note that we do not cover molecular evidence for evolution in this lab.

   Relevant lecture information: The theory of evolution
   

   Required Equipment: B Macroevolution Demonstrations

   Type	#	Per	Item	Section	Notes
   E	1	Class	Vertebrate forelimb diagrams	B Macroevolution Demonstrations	Sheets photocopied from old lab manual
   S	1	Class	Vertebrate embryo slides	B Macroevolution Demonstrations	Chick and pig embryos; 409A, 410Z
   E	2	Class	Dissecting microscopes and lights	B Macroevolution Demonstrations	for the vertebrate embryo slides
   Sp	1	Class	Frog skeleton	B Macroevolution Demonstrations
   Sp	1	Class	Bird skeleton	B Macroevolution Demonstrations
   Sp	1	Class	Cat skeleton	B Macroevolution Demonstrations
   Sp	1	Class	Human skeleton	B Macroevolution Demonstrations
   E	1	Class	Fossil boxes: 3 different Eras	B Macroevolution Demonstrations

   So=Solution, S=Slide, Sp=Specimen, L=Living, E=Equipment

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A printable syllabus, with course dates, required materials, grading and other policies can be found here.

A one page printable version of the schedule can be found here.

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