Lab 8 Population Genetics 

Introduction
G.H Hardy and
W. Weinberg developed a theory that evolution could be described as a change of
the frequency of alleles in an entire population.
In a diploid organism that has gene a gene loci that each contain one of
two alleles for a single trait t the frequency of allele A is represented by the
letter p. The
letter q represents the frequency of the a allele.
An example is, in a population of 100 organisms, if 45% of the alleles
are A then the frequency is .45.
The remaining alleles would be 55% or .55.
This is the allele frequency.
An equation called the Hardy Weinberg equation for the allele frequencies
of a population is p^{2+ }2pq+ q^{2} = 1. P represents the A
allele frequency.
The letter q represents the a allele.
Hardy and Weinberg also gave five conditions that would ensure the allele
frequencies of a population would remain constant.
The
breeding population is large. The
effect of a change in allele frequencies is reduced.
Mating is random. Organisms
show no mating preference for a particular genotype.
There
is no net mutation of the alleles.
There is no
migration or emigration of organisms.
There is no natural selection.
Every organism has an equal chance for passing on their genotypes.
If
these conditions are met then no change in the frequency of alleles or genotypes
will take place.
A simple class experiment will take place to serve as model of the evolutionary process in a stimulated population. This experiment is great in order to test a few of the basic parts of population genetics. In the experiment the class will place a piece of paper in their mouth to see if they can taste the chemical PTC which is phenythiocarbamide. People with the alleles AA, which is homozygous, and Aa, which is heterozygous, will be able to taste the PTC. People that can’t taste PTC are aa.
Hypothesis
By
allowing a class to see if they can taste PTC and recording the results the
Hardy Weinberg equation can be used to determine the allele frequencies of
the class.
Materials
The materials used in this experiment are as follows: strips of PTC test
paper, paper and a pencil.
Methods
Begin by placing a piece of the PTC test paper in
your mouth. Tasters will have a
bitter taste in their mouth. The
frequency of tasters (p^{2 }+2pq) is a found as a decimal by dividing
the total number of tasters by the total number of students in the class.
The frequency of nontasters (q^{2 }) is found by dividing the
number of tasters by the number of people in the class.
Using the Hardy Weinberg equation the frequency of
p and q can be found. q is
found by taking the square root of q^{2}.
p is found by using the equation 1q=p. Also calculate the frequencies of
the North American population. Finally
find 2pq that represents the percentage of the heterozygous tasters in the
class. Record the results in table
8.1
Results
Table 8.1 Phenotypic Proportions of Tasters and Nontasters and
Frequencies of the Determining Alleles

Phenotypes 
Allele
Frequencies 

Tasters P^{2} + 2pq^{ } 
Nontasters Q^{2} 
p 
Q 

Class
Population 
# 
% 
# 
% 
.53 
.47 
7 