The four evolutionary forces are natural selection, gene flow, genetic drift, and mutation. Charles Darwin and Alfred Russell Wallace independently developed the theory of evolution by natural selection. Natural selection is the process by which organisms best adapted to their environment tend to survive and pass on their genes more than others. Mutation introduces new genetic variation, while genetic drift and population bottlenecks can cause changes in allele frequencies in small, isolated populations. The evolutionary force that causes the fastest change in gene frequency is natural selection because it can eliminate entire traits from a population. Sickle cell anemia is caused by a mutation in the hemoglobin gene and is maintained in some populations because it provides resistance to malaria.

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1. What are the four evolutionary forces?
The four evolutionary forces are:
 Natural selection
 Gene flow
 Genetic Drift
 Mutation
2. Which two individuals independently formed a unified theory of evolution?
The two scientists that independently formed a unified theory of evolution are Charles
Darwin and Alfred Russell Wallace.
3. Briefly summarize natural selection.
Natural selection is the process that organisms go through in adaptation this is within
their environment in order to survive and produce more offspring. Within all
populations of a species, more off springs and individuals are produced than can
survive. There is variation in the different populations and competition for the limited
resources available. There are other factors that limit survival such as death from
disease, predation among others. Those best adapted to their environment, because of
their inherited traits, will be more likely to survive to reproductive age and to reproduce
than those that are less well adapted. Therefore, the genes coding for the well adapted
traits will be passed onto the next generation in higher numbers than the genes for the
less well adapted traits. Thereby, a change in gene frequency, and thus evolution will

2. have occurred. For the Natural selection process to have occurred traits must be
variable and heritable.
4. What is fitness?
Fitness is the reproductive success of any variation which will change as the
environment changes.
5. What is mutation?
The process of mutation occurs at the DNA level. It is a heritable change in the genetic
material (DNA). It is the only evolutionary force to produce a new variation. The
mutation rates in different populations are slow and they rarely have a great effect on
gene frequency change by themselves. Nonetheless, a new variation, followed by one or
more other evolutionary forces, can change gene frequency quite rapidly.
6. What is gene flow?
Gene flow is the process of movement of genes from one population to another. It
occurs constantly among populations within a species when individuals move from one
population to another.
7. A small group of people shipwreck on an island many miles from civilization where
there is no cell phone signal. When it appears that they will never be rescued, they decide
to establish their own population and begin to marry and pro- duce children. Because
there are so few of them, their gene pool is not very diverse and thus does not represent
the larger population they came from. This would be an example of which evolutionary
force?
This is an example of genetic drift. This is due to the limited number of gene variants
in the population.

3. 8. To which evolutionary force does the saying “survival of the fittest” apply?
The phrase survival for the fittest applies to Natural Selection
9. In which evolutionary force does competition play the biggest role?
Competition plays the biggest role in Natural Selection.
10. Which evolutionary force introduces new variation into the gene pool?
Mutation introduces a new variation in the gene pool.
11. Which evolutionary force is capable of changing gene frequency the fastest? Why?
Natural selection will cause the fastest change in gene frequency. This is because
environmental pressure and changes can cause elimination of an entire trait in a
population over a short period of time. Unlike genetic drift that takes some time but
only cause’s changes in a small population, and mutations occur though rarely and
take an extremely long time to show its effects on the allele gene frequency. Therefore,
natural selection is the fastest way.
12. One form of genetic drift is population bottleneck. Briefly explain it with a real or
hypothetical example.
Genetic drift usually leads to some big losses of genetic variation for small
populations. Population bottlenecks occur when a population's size is reduced for at
least one generation. The Bottleneck Effect may occur when for instance when there is
a disaster and it reduces the population to a small handful that usually does not
represent the actual genetic makeup of the initial population. Therefore, leaving the
smaller variation among the surviving individuals.
13. How may founder effect and population bottleneck be similar to a “sampling error”?

4. The founder effect and population bottleneck is similar to a sampling error in that the
smaller the sample the less likely the representative sample of the population at large.
Therefore the genes in the population of the “found” new population will not represent
accurately the frequency of the genes in the population at large, called the parent
population. The parental gene frequency will exhibit fewer differences in a larger
population than in a smaller population. This shows the similarity of the smaller
population and the sampling error.
14. What is the genetic cause of sickle-cell anemia?
Sickle cell anemia is caused by a mutation in the hemoglobin-Beta gene found on
chromosome 11.Hemoglobin usually transports oxygen from the lungs to other parts of
the body. Normal red blood cells with normal hemoglobin (hemoglobin-A) are smooth
and round and glide through blood vessels. While in abnormal hemoglobin molecules
in people with sickle cell anemia (hemoglobin S) stick to one another and form long,
rod-like structures which form a sickle shape.
15. What is the disease prevalent in many parts of Africa that helps to maintain the sickle-
cell allele in populations there?
Malaria has an association with sickle cell.
16. If two parents are both heterozygous for the sickle-cell trait, what is the probability of
having an offspring with sickle- cell anemia?
The probability is 1:4 which is a 25% chance to developing sickle cell anemia.
Make a Punnett square for this question.

5. A S
A AA AS
S AS SS
AS- Parents carry the sickle cell trait – Heterozygous
AA – 25 % chance: Offspring is normal without sickle cell disease or trait.
AS- 50% chance: Offspring has sickle cell trait
SS- 25 % chance: Offspring has sickle cell disease
17. The higher frequency of the sickle-cell allele in African Americans than in most other
U.S. groups is due primarily to the past action of which evolutionary force?
The high frequency of Sickle cell Anemia has an association with malaria provides an
excellent example of how all four evolutionary forces combined to result in a situation
that exists today. Nonetheless, nutation is the primary evolutionary force that has
caused the increased in frequency. The higher sickle cell anemia rates in African
Americans than in most other subpopulations is significant as the sickle cell allele is
provided by additional types of hemoglobin mutations in malaria infected regions of
the world.