Period 8 AP Bio

Ms. Dahle

September 12, 2011

TITLE: Population Genetics and Evolution Within a Gene Pool

INTRODUCTION: The Hardy-Weinberg scheme is a way of viewing evolution as changes in the frequency of alleles in a population of organisms. If A and a are alleles for a particular gene and each individual has two alleles then p is the frequency of the A allele and q is the frequency of a alleles. The frequency of the possible diploid combinations is expressed in the equation p2+2pq+q2=1. In order for the Hardy-Weinberg equation to work five conditions must be met: 1. The breeding population must be large.

2. Mating must be random.

3. There must not be mutations of the alleles.

4. No differential migration may occur.

5. All allele combinations must survive equally.

If the conditions are met then the allele genotype frequencies in a population remain the same. HYPOTHESIS:

8A: If we use PTC paper to determine the allele frequencies for the dominant and recessive alleles in our classroom population, then we can use the Hardy-Weinberg equation to determine the number of homozygous dominant, heterozygous, and homozygous recessive individuals. 8B: If the requirements for the Hardy-Weinberg equation are met, then the predictions of the allele frequencies by the Hardy-Weinberg equations will be similar to the actual allele frequencies. MATERIALS:

8A:

~PTC paper

8B:

~Note cards

PROCEDURE:

8A:

1. Using the PTC paper, rip off a piece and press it to the tip of your tongue. PTC tasters will sense a bitter taste. These individuals are considered tasters. 2. A number representing the frequency of tasters (p2+2pq) should be calculated by dividing the number of tasters by the total number of students. A number representing the frequency of nontasters (q2) should be obtained by dividing the number of nontasters by the total number of students. 3. Use the Hardy-Weinberg to determine the frequencies of the dominant (p) and recesive (q) alleles. The frequency of q can be calculated by taking the square root of q2. once q is determined, p can be found by the equation 1-q=p. 8B:

Case I

1. Turn the cards over so that the letters do not show, shuffle them, and take the card on top. The partner should do the same thing. Put the cards together, they represent the alleles of the first offspring. Record the genotype. Reshuffle until each partner has one offspring. 2. Both partners should record their genotype. They are now the next generation. 3. Each partner should obtain cards that correspond with the genotype. Randomly seek other people and mate with them to produce offspring of the next generation. Record genotype after each generation. 4. Calculate the allele frequencies of the population after five generations of random mating.

Case II

1. Start again with the same initial genotype and produce offspring the same way as case I. Everytime the offspring is aa it will not survive. Retry mating until AA or Aa phenotype occurs. 2. Proceed through five generations selecting against homozygous recessive offspring. Calculate the new allele frequencies.

Case III

1. Keep everything the same as Case II. If the offspring is AA flip a coin, if it is heads the individual does not survive. 2. Simulate five generations, keeping the same initial genotype. The genotype aa does not survive. The same parents must retry until an offspring that survives is produced. Calculate the new frequencies. 3. Starting at the F5 generation go through five more generations and calculate the new frequencies. Case IV

1. Divide the lab into small populations.

2. Go through five generations inside the new populations. Record the new frequencies.

RAW DATA: See lab manual

DATA:

8A:

| Phenotypes| Allele Frequency Based on the H-W Equation| | Tasters (p2 + 2pg)| Nontasters (p2)| p| q|

Class Population| #| %| #| %| .46| .54|

| 10| 71| 4| 29|...

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