Melissa Amador
AP Biology
December 15, 2013
Hardy-Weinberg Lab Report
Introduction:
This experiment was created on the basis of one we did as a class about the
differences in reproducing populations on the account of what the genotype of the
starting population was. For most of the experiments the beginning genotype for all of the
individuals would be heterozygote. The first test run, we all reproduced with nothing
stopping us. In the second run homozygous recessive was at a disadvantage, which made
sure none of the final genotypes were homozygous recessive. In the final run,
homozygous recessive continued to be a disadvantage that meant death, while
heterozygous meant a coin would be flipped and there would be a 50% chance of death.
Many of the experiments were made with a disadvantage set in the environment to
impede the genotype from being common. The experiment created for this lab was one
that was simple. We decided to just set a certain condition in the environment and allow
the population to flourish on its own.
The purpose of Hardy-Weinberg is to determine if an allele in a population is
evolving. There are 5 conditions to HW and they must all be met for the population to be
in equilibrium: no mutations, random mating, no natural selection, extreme large
populations, and no gene flow. These conditions will never be met in any population,
meaning an allele in the gene pool will always be evolving. The lab was designed the
way it was to determine how a population would evolve when there was a predetermined
genotype for all the individuals: 3 would be heterozygous and 8 would be homozygous
recessive. The expected outcome was for homozygous recessive to be the dominant
genotype in the population, homozygous dominant to not exist, and heterozygous to be
rare.
Question for investigation:
How common can heterozygous be in a small population when, homozygous recessive is
prevalent?
Hypothesis:
If homozygous recessive is prevalent, then heterozygous will be rare.
Procedure:
For this experiment, there will be 3 people with the genotype heterozygous (Aa), and 8
people with the genotype homozygous recessive (aa). Then the individuals will be
allowed to mate with whomever they want, with nothing stopping them. They will switch
cards depending on the genotype of the “baby”.
Data:
Homozygous Dominant (AA)
Heterozygous (Aa)
0
2
Homozygous Recessive (aa)
9
Analysis:
Chi Square:
A
a
a
Aa
aa
a
Aa
aa
Heterozygous: Χ2 = Σ (o-e)2/e  Χ2 = Σ (2-5)2/5 = 1.8
Homozygous Recessive: Χ2 = Σ (o-e)2/e  Χ2 = Σ (9-5)2/5 = 3.2
1.8 + 3.2 = 5.0
Hardy-Weinberg:
9/11 = .82 = q  √(.82) = .91 = q2
p2 = 0.0
2pq = .9
The data shows that the allele for homozygous recessive will be most common in the
population because it was the most prominent allele in the gene pool in the beginning
before any reproducing occurred. Homozygous dominant will never happen as a
genotype in the gene pool because the dominant allele is non-existent in the pool.
Conclusion:
The hypothesis for this experimented fully by the data received. It was supported because
it showed that the population would never be homozygous dominant because the
dominant genotype isn’t available in the gene pool. Heterozygous will be considered a
rare genotype within the population because it isn’t common and in the beginning of the
experiment the majority of individuals’ genotypes were homozygous recessive.
Populations of species may work this way and completely exclude an allele from the gene
pool and make it impossible for it to show up in the genotypes of the population.
Discussion:
From the lab I learned how Hardy-Weinberg equilibrium would never be met in any
environments or populations because there will always be a stressor that makes the
“genotypes” sway towards a certain genotype that is favorable in the environment. Some
changes I would make would be the amount of people we had. If it were possible to have
more people in the experiment we would be able to research more into rare alleles and
how common they would be at the end of reproducing for several generations. If the
group were bigger, we would have allowed for homozygous dominant to make an
appearance but with such a small group, we wanted to show how a rare allele will only
become rarer in a population, and we did.