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This simulation assignment takes about three hours. The activities are broken down into five exercises, each of which can be done independently. Please submit the answers to the questions for...

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Q1. If the frequency of the HbS allele is 0.8 in a population, what is the frequency of the HbA allele (assuming
this is a two-allele system)?
Q2. In the case study in this lab, which genotype is represented by "2pq" in the Hardy-Weinberg equation?
HAamnavrnntiec HRA

Sickle Cell Alleles assignment instruction
In the sickle cell allele exercises, you will simulate the population genetics of the sickle cell gene in relation to the occu
ence of malaria in several parts of Africa.
To complete these exercises, you will use SimBio simulation software and an accompanying workbook, which you will access online.
The workbook that comes with the software provides the theoretical background for the activities and the questions that you will complete and submit to the Tutor for grading.
Time requirement: This simulation exercise takes about three hours. The activities are
oken down into five exercises, each of which can be done independently.
Please submit the answers to the questions for all five exercises in the text file derived from the original workbook (WB).
Note: In some instances, you may need to include tables or diagrams in your answers.
In addition, submit the answers to the ten graded questions online. You will find these questions as a separate item from the exercises in the software package.
There are 10 graded questions and a written portion (WB), and both need to be provided.
SEI [01 LA [4
Assignments for:
Principles of Biology Il (2022/2023) BIOL207

AA FLEE (TT EY [p17]
12/31/25, 9:00am MST
Lab exercises are here
you fill out the questions in WB
from this.
© Sickle-Cell Alleles (WB)


: There are few questions here
Graded Questions——————
the app and submitted via app.

SimBio Virtual Labs®
EvoBeaker®: Sickle-Cell Alleles
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the associated laboratory software; however, the accompanying software license is non-transferable.
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SimBio Virtual Labs®: EvoBeaker®
Sickle-Cell Alleles
You should know that, among other things, we periodically tinker with the underlying models
in our simulations so that the results they produce (i.e. the “right answers”) change, and we let
instructors know how to recognize cheating. We hope you do not succumb to the temptation
ut, instead, go ahead and dive in. We’ve tried to make it a truly interesting experience and a fun
way to learn.
Malaria is one of the world’s most serious diseases, infecting upwards of 300 million people and
killing one and a half million people each year. It is most common in Africa but occurs in warmer
climates worldwide. People are infected when bitten by mosquitoes ca
ying certain kinds of protozoa.
The malarial protozoa are released as the mosquito’s mouth parts pierce the skin of the unlucky victim.
The protozoa then swim through the victim’s blood until reaching the liver. There they reproduce and
emerge to infect the host’s red blood cells, after which another mosquito can suck them back up and
start the cycle over again.
Just about anything that would protect people from malaria would be beneficial for those who
live in the malaria-prone areas of the world. And indeed, some people ca
y an allele of a gene that
provides just such a defense. Surprisingly, this anti-malaria allele was tracked down through studies of
a seemingly completely unrelated disease: sickle-cell anemia. Sickle-cell anemia is every bit as nasty
as malaria. Individuals with this disease have red blood cells that curve into a sickle shape instead of
emaining in the circular doughnut shape of normal red blood cells. The sickle-shaped cells tend to get
stuck in small blood vessels, blocking blood flow, and halting the supply of oxygen to downstream cells.
Unlike malaria, sickle-cell anemia is a genetic disease. Individuals inherit alleles that cause the disease
from their parents. Sickle-cell anemia is associated with a gene that encodes part of the hemoglobin
molecule (called the Hb gene). Hemoglobin is the protein in red blood cells that ca
ies oxygen. The
SimBio Virtual Labs® | Sickle-Cell Alleles
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allele for the normal hemoglobin protein is called HbA and the allele for sickle cell anemia is called HbS.
People who inherit the HbS allele from both parents (i.e., have the “homozygous” genotype HbS/HbS)
have a form of hemoglobin that makes their red blood cells highly prone to becoming sickle-shaped.
People who inherit one sickle-cell and one normal hemoglobin allele (i.e., have the “heterozygous”
genotype HbS/HbA) can experience health effects but often the effects are so minor that these people
do not realize they ca
y the HbS allele.
Although people with sickle-cell anemia typically die from the disease before they are old enough to
eproduce, it is relatively common in some parts of the world. Why doesn’t natural selection eliminate
the disease gene? The answer is that although the sickle-cell allele can cripple your red blood cells, it
can also protect you against malaria. Having one copy of HbS (the sickle-cell allele) protects you from
ecoming sick from malaria. Heterozygous (HbS/HbA) red blood cells that become infected with the
malaria protozoa will sickle. The body’s immune system recognizes that something is wrong with the
sickled cells and disposes of them. So anyone who is heterozygous for the sickle-cell hemoglobin allele
is protected from both malaria and sickle-cell anemia. In genetics lingo, this is an example of a case of
“heterozygote advantage.”
SimBio Virtual Labs® | Sickle-Cell Alleles
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Some Important Terms and Concepts
Population Genetics
The study of how the genes in populations change over time.
Genes, Loci, Alleles, and Gene Pools: A Quick Review of Terms
Genes are units of hereditary information composed of DNA (or sometimes RNA) sequences. Genes
are found on chromosomes. The place along the chromosome where the gene is located is called the
locus (plural=loci). Population geneticists often refer to genes as “loci”. Alleles are alternate versions of
genes (they have different DNA sequences which may or may not code for different proteins). The total
collection of genes in a population is called a gene pool. Population geneticists often focus on subsets
of gene pools, such as all of the alleles at a particular locus.
The Hardy-Weinberg Equation
In 1908 an English mathematician (G.H. Hardy) and a German physician (W. Weinberg) independently
developed a formula that can be used for estimating allele frequencies from genotype frequencies or
to estimate genotype frequencies from allele frequencies (for sexually-reproducing organisms). The
p2 + 2pq + q2 = 1
commonly refe
ed to as the Hardy-Weinberg equation, applies when there are two alleles of a gene.
The frequency of one allele is designated p and the other is designated q. The first part of the equation
(p2) gives the frequency of homozygotes of the first allele, the middle part (2pq) gives the frequency
of heterozygotes, and the third part (q2) gives the frequency of homozygotes of the second allele
(note: sometimes these are refe
ed to as “Hardy-Weinberg proportions”). If you know any one of the
three parts, you can deduce the other two because p + q = 1 (and thus p=1-q and q=1-p). For example,
if you know the frequency of homozygotes for the first allele in a population (perhaps because
all homozygotes for that allele have a distinctive trait), then you know p2. By taking the square root
of that, you get p and by subtracting that value from 1 you get q. Once you know p and q, you can
then plug those numbers into the Hardy-Weinberg equation to figure out the expected frequency of
heterozygotes (2pq) and homozygotes for the second allele (q2).
SimBio Virtual Labs® | Sickle-Cell Alleles
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The Hardy-Weinberg Theorem and Hardy-Weinberg Equili
The Hardy-Weinberg equation resulted from Hardy and Weinberg applying probability theory to basic
Mendelian genetics. Theoreticians often apply certain “assumptions” in their models to simplify the
underlying mathematics. Hardy and Weinberg assumed that populations are very large and that there
is no immigration or emigration. They also assumed that individuals mate at random to produce the
next generation. Given these conditions, and no mutations or selection, there will be no evolution, and
populations will be at what is known as “Hardy-Weinberg equili
ium”. The frequency of any allele in a
population will be the same as the frequency of that allele in the haploid gametes (the eggs and sperm)
and all that will happen from one generation to the next is that the alleles will be randomly shuffled
and sorted again into pairs. Given this scenario, the probability of the various combinations of alleles
(genotypes) will depend entirely on the allele frequencies.
One way to think about the Hardy-Weinberg theorem and Hardy-Weinberg equili
ium is to
imagine a system in which alleles (e.g., A and a) are drawn in pairs from a pot. The pot contains
the same allele frequencies as were present in the previous generation. This pot automatically
eplaces what is drawn from it so that the allele frequency composition remains constant.
Applying probability theory, the chance of producing a genotype is the probability of drawing
the first allele times the probability of drawing the second allele. If we substitute in p for the
frequency of A and q for the frequency of a, the probability of A/A will be (p)(p) = p2. The probability
of A/a will be (p)(q) and of a/A will be (q)(p) so the probability of a heterozygote (A/a or a/A) will be
(p)(q)+ (q)(p) = 2pq. The probability of a/a will be (q)(q) = q2. The three probabilities must add up to 1 so
p2 + 2pq + q2 = 1. This is how Hardy and Weinberg derived their famous equation.
Deviations From Hardy-Weinberg Equili
Natural Selection and Genetic Drift
As described in the previous section, the Hardy-Weinberg theorem applies to large, random-mating
populations that do not experience mutation, migration, natural selection, or random genetic drift.
Given that many populations in the real world probably don’t conform to those rules, you might
wonder about the utility of the Hardy-Weinberg theorem. The power of the Hardy-Weinberg theorem
is that it allows us to quantify our expectations of what would happen in populations if evolution were
not occu
ing, which allows us to compare those expectations to what we see in real populations. For
example, if we suspect natural selection is acting on a particular allele or genotype in a population,
we can determine allele and/or genotype frequencies in the population in one generation and then
see how well the frequencies conform with the expectations of Hardy-Weinberg equili
ium in future
generations. If the frequencies are not very different than the expected Hardy-Weinberg proportions,
SimBio Virtual Labs® | Sickle-Cell Alleles
© 2022, SimBio. All Rights Reserved. 5
that would be evidence that natural selection is not acting on that allele or that the selection pressure is
too weak to detect with our data.
Genetic drift: the changes in allele frequencies that are due to chance events. Genetic drift is another
major factor that causes populations to evolve and thus deviate from Hardy-Weinberg equili
While natural selection always has a positive effect by favoring the disproportionate propagation of
eneficial alleles or genotypes, genetic drift can have a positive, neutral, or negative effect. Genetic drift
is most pronounced when a population is small, because that is when chance events dominate. Going
ack to the “pot of alleles” example in the last section, imagine we need to create 1,000 populations
of only 5 individuals each by drawing from the bottomless pot of alleles that was generated by the
previous generation’s gametes. There will be a lot of variability in allele and genotype frequencies
among those populations due to chance (like flipping a coin and getting 4 tails in a row). If any one
of the small populations is used as the basis for a new bottomless pot of alleles, the next generation
would likely be quite different than the previous one.
Answered 2 days After Feb 15, 2024


Dr Shweta answered on Feb 16 2024
10 Votes
PDF solutions:
Exercise 1
5.1 When the HbS allele frequency goes up, the HbA allele frequency goes down
5.2 The two allele frequencies add up to, p+q= 1
6.1 frequency of sickle cell allele 0.39
6.2 frequency of the normal hemoglobin allele 0.61
6.3 malaria deaths in the past five years 22
6.4 sickle-cell deaths in the past five years 58
7.1 allele frequencies and number of deaths = 0
Exercise 2
1.1 hardy Weinberg equation: p2 +2pq+q2 = 1
2.1 genotype represents:
p2    =    dominant homozygous frequency (AA)
2pq    =    heterozygous frequency (Aa)
q2    =    recessive homozygous frequency (aa)
2.2 Genotype of people with sickle cell anaemia: HbsHbs
3.1 Proportion of the population with sickle-cell anemia 0.13
3.2 expected frequency of the HbS allele in the population 0.36

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