Natural Selection in Teddy Grahams
Introduction
You are a bear-eating monster. There are two kinds of bears that you like to eat: happy bears and sad bears. You can tell the difference between them by the way they hold their hands. Happy bears hold their hands high in the air, and sad bears hold their hands down low. Happy bears taste sweet and are easy to catch. Sad bears taste bitter, are devious and hard to catch. Because of this you only eat happy bears. The happy trait in bears is caused by the expression of a recessive allele. The homozygous recessive condition is being happy. The sad trait is caused by a dominant allele. New bears are born every year (when they are hibernating in their den, the cardboard box), and the birth rate is one new bear for every old bear left from last year.
Materials:
Teddy Bear Grahams, lab worksheet, pencil
Procedure:
1. Obtain a population of 10 bears and record he number of happy and sad bears and the total population number. Using the equation for Hardy-Weinberg equilibrium, calculate the frequencies of both the dominant and recessive alleles and the genotypes that are represented in the population. Example: If 5 of the 10 bears are happy, then 10 out of 20 alleles would be happy alleles. Therefore the q2 number would be 0.5. You must then determine the q number by taking the square of 0.5.
2. Now, go hunting! Eat 3 happy bears. (If you do not have 3 happy bears then eat the difference in sad bears.)
3. Once you have consumed the bears obtain a new generation from your den (the box). You should only remove seven additional bears from the den for a total of 14 bears.
4. Repeat the procedures again. Be sure to record the number of each type of bear and the total population.
Table:
| Generations | P2 (sad) | 2pq (sad) | q2 (happy) | P | q |
| 1. Initial | |||||
| 2. | |||||
| 3. | |||||
| 4. |
Questions:
1. Describe what is happening to the genotype and allele frequencies in the population of Teddy Grahams?
2. What would you expect to happen if you continued the selection process for additional generations?
3. How would the frequencies change if you were to now select for the sad bears?
4. Why doesn’t the recessive allele disappear from the population? How is it protected?
