Experiment - Curling DNA

Understanding the Gene Pool

Purpose:
You will make a model gene pool based on an initial assumed population, collect data to test the Hardy-Weinberg principle, compare your data to predictions in a cross-multiplication table, and use a model gene pool to examine the change in allele frequencies caused by harmful genotypes in a given environment.

Supplies:
2 small bowls or cups
60 red beans
140 white beans

Label one bowl or glass as “male gametes” and one as “female gametes.” Count out 30 red beans and 70 white beans and place them in one of the bowls. Mix the beans. Place another 30 red beans and 70 white beans in the second bowl. Mix the beans. The red beans represent the dominant allele for brown coat color (B) in rabbits; the white beans represent the recessive allele for white coat color (b).

On another sheet of paper draw a cross-multiplication table. Complete the table to calculate the expected frequency of red and white alleles in the population.

Without looking at the beans, reach into each bowl and draw out one bean.

Record what combination of beans you drew. After you record the result, place each bean back in the bowl from which it came. Mix the beans.

Repeat another 49 times and record your results.

Suppose that homozygous dominant individuals cannot survive to reproduce. Look at your data table to see how many homozygous dominant individuals you drew out. Remove one half that number of red beans from each bowl. Each bowl now represents the gene pool of the second generation. Draw another data table and label it “second generation” and repeat the procedure of drawing beans 50 times.

Results, Questions:
1. What did each pair of beans you drew out of the bowls represent? (the genotype of one offspring from the population)

2. How do the results of your first 50 draws compare with the frequencies predicted in your cross-multiplication table?

Applications:
1. What happened to the allele frequencies in the second generation when homozygous brown rabbits were selected out of the population?

2. Do your results support the Hardy-Weinberg principle?