A Copy of This Lab Is Available on Canvas If You Need to Reference These Instructions

CLASS SET

A copy of this lab is available on Canvas if you need to reference these instructions.

Modeling Gene Flow and Genetic Drift

Genetic drift and gene flow sound alike when you hear them described, and it can be difficult to distinguish between them just based on a definition. The objective of this activity is to distinguish between the two and to observe how gene flow and genetic drift can affect the allele frequencies of a population.

• Genetic drift is when the allele frequency of a population is changed due to randomness or chance.
• Gene flow is when alleles travel from one population to another population of the same species. It can also be called migration.

In this simulation, you will follow a population of tropical beetles through a series of events and track the frequency of the alleles of one of its genes. The gene you will be following controls the beetle’s color by determining the amount of pigment (a protein!) deposited in its cuticle (the outer layer of the exoskeleton). The gene has 2 alleles (A and a) and 3 phenotypes (black (genotype AA), grey (genotype Aa), and light (genotype aa)).

Procedure:

Part 1: Determining Allele and Genotypic Frequencies (Percents) in a Population

1. Start by turning all of the beetles right side up. Count how many beetles TOTAL you have in your initial population. Record the number on the data sheet. Beetles are diploid, therefore multiply the beetle population size by 2 to determine the TOTAL number of alleles (gene pool size). Record the number on the data sheet.

1. Determine the relative genotype frequency of your population: Count the number of bugs with the AA, Aa, and aa genotype and record your results in Table 1 under the appropriate column. You should count each beetle once. The number of AA plus Aa plus aa should add up to your TOTAL population.

1. Next, determine the relative allele frequency of your population: Count each allele (A and a) separately and record your results in Table 2 under the appropriate column. You should count 2 alleles per beetle. The number of A plus a that you count should add up to your TOTAL number of alleles.
   

Part 2:

Your tropical beetle population experiences a severe weather event. A typhoon blows 8 of your bugs to a remote island off the mainland! Which bugs get blown to the island is random, so before you choose which bugs will make up your new population, turn them over so you can’t see their genotype or their phenotype.

1. After you’ve turned your bugs over and shuffled them around face down, randomly select 8 bugs and put the rest away. These 8 are your new island-dwelling population. They are the founders of a new colony.
   
2. Now, flip your 8 island-dwelling bugs over and repeat steps 1-3. Record your results in the data tables in the column labeled Founding Population.

Part 3:

Put your 8 bugs in your island population back in your main population so you again have your initial population size again. Each lab table is a different population. Some adventurous bugs are going to travel. Flip your bugs over so you can’t see their genotype or their phenotype. Then, exchange 10 randomly selected bugs with another group. This represents migration which includes both emigration (leaving) and immigration (entering).

1. After the exchange, flip your bugs right-side up again and repeat steps 1-3 with all the bugs (your remaining ones plus the immigrants). Record your results in Tables 1 & 2 under the column labeled Migrating Population.
   

CLEAN-UP:

When you are finished recording your data, return your immigrant bugs to the group you exchanged with. Make sure all your bugs are accounted for and are the right color and put them back in their container.

Complete the Analysis section of the lab at your desk. You will need a calculator.

Name ______DUE Date ______Period ______

Modeling Gene Flow and Genetic Drift

Data:

beetle population size ______

beetle gene pool size (total number of alleles) ______

 Is your gene pool size equal to your population size X 2? If your answer is no, read the procedure again!

Table 1. Beetle Genotype/Phenotype Counts

Initial Population Founding PopulationMigrated Population

Genotype/Phenotype (Part 1) (Part 2)(Part 3)

Table 2. Beetle Gene Pool Allele Counts

Initial Population Founding PopulationMigrated Population

Allele Counts (Part 1) (Part 2)(Part 3)

Analysis

Frequency is defined as a measure of how common something is. Frequency is expressed mathematically as a decimal calculated by dividing the part by the whole, just like your grades. In this lab, you will determine the frequency of each genotype/phenotype as well as the frequency of each allele. Frequencies always add up to 1. The formulas to calculate this are given below. Record the frequencies in the analysis tables below.

genotype/phenotype frequency = # beetles with genotype/phenotype

population size

allele frequency = # of the allele in the gene pool

gene pool size

Table 3. Beetle Genotype/Phenotype Frequencies

Genotype/Phenotype Frequency in Initial Population Frequency in Founding Population Frequency in Migrated Population

Table 4. Beetle Gene Pool Allele Frequencies

Allele Frequency in Initial Population Frequency in Founding Population Frequency in Migrated Population

Conclusion:

Answer the following questions after cleaning up your lab table.

1. Based on the description given for the gene, which pattern of inheritance (sex-linked, incomplete dominance, or codominance) does it exhibit? ______

1. When the typhoon carries some beetles to an island, is that an example of genetic drift or gene flow? ______

1. When the typhoon carries some beetles to an island, is that an example of the bottleneck effect or of the founder effect? ______

1. When the some beetles venture out to other populations, is that an example of genetic drift or gene flow? ______
   
2. Did your beetle population get darker or lighter if you compare the phenotypes of the initial population to the phenotypes of the founding population? ______

What happened to the gene pool that resulted in this change? ______

1. If you did the simulation again, would you expect similar results? ______
   Why or why not? ______
   
2. If the two populations change (evolve) separately long enough, eventually they will be two different ______and no longer able to ______together.

1. Evolution is defined as a change in gene frequency. Did your population evolve from the initial population to the founding population? ______

Explain. ______

Did your population evolve from the initial population to the migrating population? ______Explain. ______

1. Based on your observations in this lab, does evolution occur in individuals or in populations? ______Explain. ______