BIOL222 Unit 2 Exam - Most black bears

Genetic Queastion

Unit 2 Exam Take-Home Portion

 BIOL 222 Spring 2024

Complete the questions below and submit by Tuesday, April 2. 15 points

1. (5 point) Most black bears (Ursus americanus) are black or brown in color. However, occasional white bears of this species appear in some populations on island along the coast of British Columbia. Researchers determined that white coat color in these bears results from a recessive mutation (G) in the melanocortin-1 receptor locus (mcr1), the same locus responsible for red hair in humans. The wild-type allele at this locus (A) encodes black or brown color. Samples from bears on three islands were collected and their genotypes at the mcr1 locus was determined: Genotype Number

AA   42

AG   24

GG   21

A. What are the frequencies of the A and G alleles in this population of bears?

B. Give the genotypic frequencies expected if the population is in Hardy–Weinberg equilibrium.

C. Is it reasonable to predict that in a population of black bears in Shenandoah National Park, you would expect to see the same frequency of white bears as you calculated in part B? Briefly explain why or why not.

2. (10 points) PopGen Fish Pond is an online simulation that allows you to explore how different factors of the Hardy-Weinberg equilibrium can contribute to changes in allelic frequencies in a virtual koi pond. Launch the PopGen Fish Pond simulation here: http://virtualbiologylab.org/population-genetics/

For a brief review of the Hardy-Weinberg model and the principles that maintain equilibrium, as well as a primer on koi genetics, read through the background on the model. Run through the tutorial to get familiar with the simulation features.

 Introduction to the Simulation

A. Look over the experimental design. Which parameters do you expect to affect allele frequency the most? Relate them to Hardy-Weinberg equilibrium in your answer.

B. What factors do you expect to affect equilibrium the least? Why? Population Demographics

C. Set the initial population size to 200, carrying capacity to 400, sex-ratio to 0.5, mortality rate to 10, brood size to 10, and initial ‘R’ Allele to 0.

5. Leave all other settings at default. Run the simulation for at least 150 generations. Go “To Data” to view the data collection. Speed up simulator to 16X by selecting the forward button five times.

• What does it mean that the ‘R’ Allele is set to 0.5?

• What is a carrying capacity?

• How do the allele proportions change over time?

D. Raise the initial ‘R’ allele proportion 0.8. Run the simulation for at least 150 generations.

• What happens to the ‘rr’ individuals over time?

• What happens to the ‘r’ allele over time? Evolutionary Parameters: Mutation Rate

E. Return the initial ‘R’ proportion to 0.5, and raise the R to r mutation rate to 0.01. Run the simulation for at least 150 generations. How do the allele proportions change over time?

 F. Now lower the carrying capacity to 50. How do the allele proportions change over time?

G. What impact does mutation have on allelic frequencies? Does carrying capacity affect this? Why or why not? Evolutionary Parameters: Migration

H. Raise the migration rate to 0.5 and set the migrant ‘R’ proportion to 0.5. Return the carrying capacity to 400 and the mutation rate to 0. Run the simulation for at least 150 generations. How do the allele proportions change over time? Why?

I. Raise the migrant ‘R’ proportion to 0.9. Run the simulation for at least 150 generations.

• How do the allele proportions change over time? Why?

• What impact does migration have on allelic frequencies? What factors affect this? Evolutionary Parameters: Fitness J. Return the migration rate to 0. Lower the relative fitness of ‘rr’ to 0.5. Run the simulation for at least 150 generations. How do the allele proportions change over time? Why? K. Lower both the fitness of ‘RR’ and ‘rr’ to 0.5.

• How do the allele proportions change over time?

• How do the genotype proportions change over time?

• Are your answers to the last two questions different? Why or why not? L. Did any the effect of any of the factors you changed surprise you?