Hardy Weinberg Problems
1. In Drosophila, the allele for normal length wings is dominant over the allele
for vestigial wings. In a population of 1000 individuals, 360 show the
recessive phenotype. How many individuals would you expect to be
homozygous dominant and heterozygous for the trait. 160 individuals are
homozygous dominant and 480 are heterozygous.
2. The allele for the ability to roll one’s tongue is dominant over the allele for the lack of
this ability. In a population of 500 individuals, 25 percent show the recessive
phenotype. How many individuals would you expect to be homozygous dominant and
heterozygous for this trait? 125 are homozygous dominant and 150 are heterozygous.
3. The allele for the hair pattern called widows peak is dominant over the allele for no
widow’s peak. In a population of 1000 individuals, 510 show the dominant phenotype.
How many individuals would you expect of each of the possible three genotypes for this
trait? 510 are AA, homozygous dominant, 410 are Aa heterozygous, and 80 are aa,
homozygous recessive.
4. In the United States, about, 16 % of the population is Rh negative. The allele for Rh
negative is recessive to the allele for the allele Rh positive. If the student population of a
high school in the U.S. is 2,000, how many students would you expect for each of the
three possible genotypes? 720 are homozygous dominant, 960 are heterozygous, and 320
are homozygous recessive.
5. In certain African countries, 4 percent of the newborn babies have sickle cell anemia,
which is a recessive trait. Out of a random population of 1,000 newborn babies, how
many would you expect for each of the three possible phenotypes? 640 are AA
homozygous dominant, 320 are Aa, heterozygous, and 40 are aa, homozygous recessive.
6. In a certain population, the dominant phenotype of a certain trait occurs 91 percent of
the time. What is the frequency of the dominant allele? The frequency of the dominant
allele is .91.
Hardy Weinberg Problems
1. In Drosophila, the allele for normal length wings is dominant over the allele for
vestigial wings. In a population of 1000 individuals, 360 show the recessive
phenotype. How many individuals would you expect to be homozygous dominant
and heterozygous for the trait.
2. The allele for the ability to roll one’s tongue is dominant over the allele for the lack of this
ability. In a population of 500 individuals, 25 percent show the recessive phenotype. How
many individuals would you expect to be homozygous dominant and heterozygous for this
trait?
3. The allele for the hair pattern called widows peak is dominant over the allele for no widow’s
peak. In a population of 1000 individuals, 510 show the dominant phenotype. How many
individuals would you expect of each of the possible three genotypes for this trait?
4. In the United States, about, 16 % of the population is Rh negative. The allele for Rh
negative is recessive to the allele for the allele Rh positive. If the student population of a
high school in the U.S. is 2,000, how many students would you expect for each of the three
possible genotypes?
5. In certain African countries, 4 percent of the newborn babies have sickle cell anemia, which
is a recessive trait. Out of a random population of 1,000 newborn babies, how many would
you expect for each of the three possible phenotypes?
6. In a certain population, the dominant phenotype of a certain trait occurs 91 percent of the
time. What is the frequency of the dominant allele?
“Hey, I said Spit that Out” Lab
An investigation using phenylthiocarbamide tasting papers and the Hardy-Weinberg equation
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 p2+ 2pq+ q2 = 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.
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.
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 (p2 +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 (q2 )
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 q2. p is found by using the equation 1-q=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
Allele Frequencies
Phenotypes
Class
Population
North
American
Population
Tasters
Nontasters
P2 + 2pq
Q2
#
%
55
#
p
Q
.33
.67
%
45
1. What is the % of heterozygous tasters 2pq in your class? Write out the complete
Hardy-Weinberg equation and show your work.
2. What % of the North American population is heterozygous for the taster
trait? Write out the complete Hardy-Weinberg equation and show your work.
3. Explain the difference or similarity between class data vs. North American data