Agents of Change Lab Activity

Agents of Change Lab Activity

In this investigation, you will design and conduct experiments to examine the influence of population size, genetic drift, and natural selection on the rate of evolution by measuring changes in allele frequencies.

Question

How do genetic drift and natural selection influence the allele frequency within a population?

Hypotheses

(a) Work with a partner to develop hypotheses to explain your predictions about how genetic drift and natural selection influence the allele frequency within a population.

Materials

beans in colour A (to represent allele R)

beans in colour B (to represent allele r)

large flask/plastic bag (to represent a gene pool)

Experimental Design

(a) Work with your partner to conduct experiments for Parts I, II, and III by using or modifying the sample procedures below. Record a complete set of steps (any changes you may make) and prepare data collection tables.

Sample Procedure (you may wish to change this)

1. Place an equal number of beans of each colour (be sure to record the total) in the plastic bag.

2. Thoroughly mix the “alleles” (beans) in the “gene pool” (bag).

3. At random, reach into the gene pool and pick out roughly half of your total, pairs of alleles to represent

offspring genotypes that contribute to the next generation.

4. Determine and record the number of each genotype (e.g., 5 RR, 7 Rr, 8 rr).

5. Record the F1 allele frequencies as decimal values. For example, divide 17 R

and 23 r by 40 to get the frequencies of 0.425 R and 0.575 r, respectively.

6. Place the next generation of 80 beans in the “gene pool” bag in the same

proportions of allele frequencies as the “offspring” (e.g., 0.425 *80 =34 R,

0.575 * 80 = 46 r).

7. Repeat steps 3–6 for four additional generations.

8. Plot a graph of allele frequency versus generation to present your data. Use

two different colours on the same set of axes to represent the R and r alleles.

Part I: Random Mating, No Selection

9. Run at least 4 generations in which you use large populations and meet the conditions of the Hardy–Weinberg principle. These trials act as your control in Part II and Part III.

Part II: Genetic Drift

10. Run at least 4 generations in which you examine the influence of population size on the degree and rate of genetic drift. Choose two or more starting populations of different sizes. As an option, you may also wish to model a founder effect.

Part III: Natural Selection

11. Run at least 4 generations in which natural selection occurs. You might model a favoured homozygous genotype in which, for example, RR offspring might be twice as successful as other genotypes. If so, you would need to allow for the increased ratio of offspring contributing to the next generation, while maintaining

a stable, large population. As an option, you could investigate selection against a homozygous lethal allele by assuming that each time a specific homozygous allele pair is selected, it dies, and you have to keep adding pairs until you have 20 offspring. Another option is to investigate a selective advantage, for a dominant phenotype.

Analysis

(a) Prepare and submit completed laboratory reports for your three investigations, including the presentation of your results.

(b) How did population size influence the degree and rate of evolutionary change? Did any alleles become fixed in a population? In what size populations might you expect it to be relatively common for alleles to become fixed? Why?

(d) How did natural selection influence the degree and rate of evolutionary change? Did any alleles become fixed in the population?

(e) Were your results unusual compared to what you would have guessed (hypothesis)?

(f) For each of your experiments in which evolution did occur, which of the five conditions of the Hardy–Weinberg principle was not met?

Synthesis

(i) Assume you introduced a single new mutant allele to your population. Explain what you expect would happen under each of the following conditions:

(i) The mutant is harmful and the population size is large.

(ii) The mutant is harmful and the population size is small.

(iii) The mutant is beneficial and the population size is large.

(iv) The mutant is beneficial and the population size is small.

(v) A beneficial mutant is introduced and the population is observed four

generations later.

(vi) A beneficial mutant is introduced and the population is observed

Expectations

This is due April 14th, 2009. It is to be a pseudo-formal write up (only one needs to be handed in per pair). You will need a title page, hypothesis for each of parts I-III, procedure for each of parts I – III, a results section with any tables and graphs you made for each section, and a discussion section. The discussion should make up the majority of your report and be in paragraph format with sub headings for each part. It should at least, contain how your results compared to your hypotheses, why you chose the procedure you did (or made any edits to the sample one), and the analysis and synthesis questions. You need not answer the questions formally (i.e. it would be preferred if you addressed the questions for each section in paragraph format).

Mark breakdown

Communication: out of 6 – for complete and logical tables/results sections including any graphs

Inquiry: out of 9 – for complete hypotheses, and all synthesis questions answered

Application: out of 9 – for complete answers to the analysis questions