Sickle Cell Anemia
- Gather the red beads, blue beads, and one 250 mL beaker.
- Imagine that you are working with the alleles that determine the expression of sickle cell anemia. “S” is dominant and “s” is recessive. SS is normal, Ss is not fatal, and ss is fatal.
- Place 25 red (S) and 25 blue (s) beads into the 250 mL beaker and mix well.
- Randomly (without looking) remove two beads. Record the allele pair you pulled by placing a tabulation mark in Data Table 3. Do not return the beads to the beaker and be sure to keep each allele pair separate.
- Repeat Step 3 ten times.
- Record how many of each allele pairing were pulled, then remove each fatal ss pairing from the population.
The remaining beads survived and reproduced. Count the remaining blue and red beads that were pulled from the beaker and place twice as many of each back into the beaker. Mix well.
- Repeat Steps 3 – 7 seven times.
- Count the number of each color bead in the container. Use these numbers to answer Exercise Question 1.
- What was the ratio of alleles at the beginning of this exercise and at the end of this exercise? Did the ratio change? If so, in favor of which allele?
- Have any alleles been selected against?
- Given enough generations, would you expect one of these alleles to completely disappear from the population? Why or why not?
- This exercise assumes that there is no genetic advantage to being homozygous dominant or heterozygous for the sickle cell allele. Do some research on these alleles. Is this the case in the real world? Why or why not?
- How would your response to Question 4 change the ratio of alleles and genotypes compared to your results in this exercise?