AP Biology Name ______
Sickle-Cell Anemia/Malaria Connection
Most people inherit one copy of the normal hemoglobin gene (hemoglobin A) from each parent and their red blood cells are round. Some individuals inherit a sickle-cell gene (hemoglobin S) from one parent and are thus carry the sickle-cell trait. There red blood cells would appear similar to the ones shown in the picture to the right with a mix of round and sickle-shaped cells. If an individual receives the hemoglobin S gene from both parents they are said to have sickle-cell anemia and often will die early in life due to various medical complications.
Simulating inheritance of the sickle-cell gene:
For each simulation: red bean = normal hemoglobin A white bean = sickle-cell hemoglobin S
Part A – U.S. Simulation
1) Place 25 red beans and 25 white beans into a paper bag.
2) Mix the beans and without looking pick two beans from the bag.
3) Repeat step 2 nine more times keeping each pair of beans separated for later.
4) For each individual that is AA (red/red) add four red beans to the bag to simulate reproduction.
5) For each individual that is AS (red/white) add one red and one white bean to the bag.
6) Do not add any beans to the bag for the SS (white/white) individuals as they died early in life from sickle-cell anemia.
7) This is the end of Round 1.
8) Count the number and color of beans in the bag, fill in the data table below and place the beans back in the bag (your total will probably not be 50 anymore).
9) Repeat steps 2-8 two more times to simulate continued reproduction of this population and passing of genes from generation to generation for Round 2, Round 3.
10) Complete data chart, complete a Hardy-Weinberg calculation, and write a conclusion describing what is happening to the normal hemoglobin A gene and the sickle-cell hemoglobin S gene in this population. Explain this trend.
Red beans (A) / White beans (S) / Total / % Red (A gene) / % White (S gene)Starting Point / 25 / 25 / 50 / 25/50 = 50% / 25/50 = 50%
Round 1
Round 2
Round 3
Note: The final percentages after each round are equal to the allele frequencies for gene A and gene S. In other words, in terms of Hardy-Weinberg, the percentage of the A gene = p and the percentage of the S gene = q. Use the Hardy-Weinberg equation to determine p2 + 2pq + q2 for the starting and final populations (after Round 3) and determine whether the population seems to be evolving.
Part B – Africa and/or Asia Simulation
1) Place 40 red beans and 10 white beans into a paper bag.
2) Mix the beans and without looking pick two beans from the bag.
3) Repeat step 2 nine more times keeping each pair of beans separated for later.
4) Do not add any beans to the bag for the AA (red/red) individuals as they died from malaria.
5) For each individual that is AS (red/white) add four red and four white beans to the bag to simulate reproduction as these individuals (heterozygotes, or carriers) are resistant to malaria.
6) Do not add any beans to the bag for the SS (white/white) individuals as they died early in life.
7) This is the end of Round 1.
8) Count the number and color of beans in the bag, fill in the data table below and place the beans back in the bag (your total will probably not be 50 anymore).
9) Repeat steps 2-8 two more times to simulate continued reproduction of this population and passing of genes from generation to generation for Round 2, Round 3, and Round 4.
10) Complete data chart, write a null hypothesis, conduct a Chi-Squared Test, and write a conclusion describing what is happening to the normal hemoglobin A gene and the sickle-cell hemoglobin S gene in this population. Explain this trend.
Red beans (A) / White beans (S) / Total / % Red (A gene) / % White (S gene)Starting Point / 40 / 10 / 50 / 40/50 = 80% / 10/50 = 20%
Round 1
Round 2
Round 3
Use the Chi-Square test to determine if the population is evolving by comparing the starting frequencies (what you would have expected if the population was not evolving) with the frequencies you observed after Round 3.
E
Hemoglobin A / 40
Hemoglobin S / 10
Conclusion:
Which simulation (US or Africa/Asia) demonstrates an example of heterozygous advantage? Explain.