NATURAL SELECTION AND GENE FREQUENCY
BY WOLFGANG
WHAT IS THAT?
• Natural selection is a key mechanism of
• Gene frequency demonstrates the
evolution.
occurrence of an allele compared to other
alleles of the same gene in a population.
• It is the process in which individuals with
certain heritable traits survive and reproduce
• The Hardy-Weinberg Principle states allele
at higher rates than other individuals without
frequencies will remain the same through
those traits.
generations in a population: with
• These traits allow them to adapt to various
extremely large in size, that randomly
environmental pressures, favoring their
mates, and with the absence of mutations,
survival and passing on of those suitable traits
gene flow, and natural selection.
to succeeding generations, thereby altering
allele frequencies.
The Natural Selection Experiment
The Hardy Weinberg Experiment
Purpose:
The natural selection lab aims to simulate the process
by which biological traits become more or less
prevalent in a population that has a changing
environment. The natural selection lab will also attempt
to show the relationship between predators and prey.
Purpose:
To create a population and demonstrate how
consistent Hardy-Weinberg's principle really is.
To observe the survival rates in genotypes and
phenotypes of a population over a span of 6
generations.
Hypothesis:
We predict that the predator will naturally pick out the
prey that is most contrasting in color to its
environment. The species that blends in the most to its
environment in color will thrive and reproduce to make
more generations of offspring.
Hypothesis:
Since there are mutations, certain allele frequencies
will decrease dramatically due to the circumstances of
the mutation standards. For other cases of mutation,
new species will emerge.
SPECIMENS & MATERIALS
The Natural Selection Experiment
The Hardy Weinberg Experiment
Specimens:
• 40 small colored paper dots which
represent the prey
Specimens:
• Red, white, and black beads which represented
alleles.
• One clawed and double clawed
predators that kill the species.
Materials:
• 1 plastic cup for the “dead” dots
Materials:
• Red beads were used to represent red alleles.
• Black beads were used to represent black alleles.
• White beads were used to represent white alleles.
• 6 cups to place different allele combination in.
• 1 petri dish lid used to place allele combinations
in.
• 2 distinct fabric mats which
represented different environments for
your dots
• A computer to record results on excel
NATURAL SELECTION METHODS
1. Provided by the instructor, obtain one of the bottles of colored
dots and gather 40 paper colored dots of one color per each
individual in your group.
2. The instructor will then provide a fabric board that will serve as
an “environment” for your species.
3. Place your colored species around the board in any order. Next,
designate a predator for each group and send them to another
environment where they will simulate the killing of a species by
“eating them” for an allotted time set by the instructor.
4. After the event has occurred, calculate how many could survive,
and add in the offspring produced in that generation to the
population .
5. Repeat this process with multiple claws, environments, and
various conditions in order to simulate natural selection.
NATURAL SELECTION RESULTS
NATURAL SELECTION ANALYSIS
The different colored dots represented the genetic variation
between species. We predicted that those species that stood
out from their environment were less likely to survive. Those
species that adapted to their environment over time had a
better chance at survival.
• Predators play a role in enforcing evolution and natural selection because they choose which populations
survive and which do not. Those species newly introduced thrive because the predators are not yet familiar
with them as shown in the previous slide the newly introduced dark green dots thrived more than any of
the other populations.
• When a population is brought into a new environment their survival may be affected. Those that once were
able to successfully survive in the old environment may not be able to adjust so quickly to the new
environment because they have not yet adapted.
HARDY WEINBERG METHODS
Case 1-2
1.
2.
3.
4.
5.
6.
7.
8.
Gather all materials and count out 50 white beads and 50 red beads.
Put the red and white beads into a single cup so that the beads will mix.
Have 3 separate cups available for your RR, Rw, and ww bead combinations.
Have a member of the group randomly grab two beads at a time and put the
appropriate bead combinations into its corresponding cup.
Once the team member has randomly picked all the beads, have someone
count and record on your excel document how many of each combination was
acquired.
Depending on which case you’re doing have a team member calculate the
amount of white beads that should be eliminated from the next generation.
Repeat steps 2-6 until you have reached generation 6.
For cases 3-4 repeat steps from case 1-2 but with different beads and
different mutation standards.
GENE FREQUENCY RESULTS: Mutation Effects
GENE FREQUENCY RESULTS: Population Percent
GENE FREQUENCY ANALYSIS
Our hypotheses were validated because the mutations affected
allele frequencies significantly. The positive mutations led to an
increase in population % whereas the negative mutations lead
to a decrease in population %. Also, new species emerged with
the introduction of the dominant black allele producing favored
phenotypes of black and dark red.
• In this population, the red allele is dominant while the white allele is recessive. The dominant phenotype of red is
selected for, represented by the homozygous dominant RR and heterozygous dominant Rw. This favored trait is
passed on to more offspring, increasing its allele frequency.
• In both cases of 67% survival and 0% survival of the white allele, its frequency decreased dramatically over
time. However, we see that it is almost impossible to eliminate the recessive alleles because of the heterozygous
Rw genotype that codes for the favored phenotype.
• Unsuccessful genotypes leads to unsuccessful phenotypes resulting in the decline of allele frequency over time.
And natural selection consistently increases the allele frequencies of of favorable phenotypes over time, leading
to adaptive evolution.
HOW ARE THEY RELATED?
• Natural selection can increase the frequencies of alleles if they are
advantageous to a species survival and reproductive abilities. If
they somehow produce a phenotype that is not a selective
advantage, their frequency will decrease.
• The change in allele frequencies is one way of defining evolution. A
population evolves as “better” alleles increase in frequency in the
gene pool.
• This means that gene frequency and natural selection go hand in
hand. They affect one another directly because the frequency of a
gene makes it better suited for natural selection, while
simultaneously, natural selection chooses which genes are going to
be selected against.
WORKS CITED
Campbell, Neil A., and Jane B. Reece. Campbell Biology. San Francisco, CA:
Benjamin Cummings, 2011. Print.
Darwin, Charles. "On The Origin of Species." The Origin of Species by Charles
Darwin. Usenet Newsgroup, n.d. Web. 17 Feb. 2015.
Photo Credits
Darwin’s Finches:
http://www1.northbrook28.net/~pamendelson/Mrs._Mendelsons_Site/Natural_Selection_Classification_files/shapeimage_3.png
Colorful Chromosomes: http://genetics.thetech.org/sites/default/files/KaryColor.gif
Natural Selection Banner: http://i.ytimg.com/vi/aTftyFboC_M/maxresdefault.jpg
Hardy Weinberg Penguins: http://i.ytimg.com/vi/oG7ob-MtO8c/maxresdefault.jpg
NS Cartoon Fish: http://media-cache-ak0.pinimg.com/736x/1d/d1/34/1dd13452486e4fd130930d50d2acbb53.jpg
Gene Frequency Goats: http://farm7.staticflickr.com/6128/5916685986_f891ba6255.jpg
Natural Selection Birds and Beetles: http://uedata.berkeley.edu//media/3/52571_evo_resources_resource_image_380_original.gif
All other photography were done by SCC Biology 3 Students