Hardy-Weinberg Equilibrium
Modeling Hardy-Weinberg Equilibrium
Introduction:
The purpose of this experiment was to determine how certain
factors effect allele frequencies in a population. The experiment was based on
the principles of Hardy-Weinberg equilibrium and factors that can drive a
population out of this equilibrium. We used Microsoft Excel sheets to create a
mathematical model to simulate a population and test the effects of certain
factors on allele frequencies. My key findings were that differing population sizes tend to
cause greater changes in allele frequencies in a small population than in a
large population over one or several generations. I also found that selection
against homozygous recessive alleles decreased the frequency of this allele
while increasing the frequency of the other allele for the gene in question
over one or many generations. This is important because it demonstrates exactly
how certain factors affect allele frequencies and demonstrate that certain
factors can cause a change in allele frequencies in one or
more generations. My major conclusions provided evidence for how forces of
microevolution operate by indicating different population sizes of large and
small populations and selection against homozygotes for a particular allele affect
allele frequencies.
I hypothesize that population sizes will have more fluctuation for allele frequencies in a small population rather than in a large population over multiple generations since allele frequencies should be more significantly altered by chance events in a small population than in a large population. I also believe that selection against homozygotes for one allele will decrease the frequency of that allele over multiple generations by reducing the number of organisms with that allele in the population and increasing the number of organisms without that allele frequency.
Materials:
I used Microsoft Excel on my surface to create the spreadsheets to model the Hardy-Weinberg Equilibrium
Methods:
To create the basic Excel spreadsheet to begin my experiment, I followed the steps from this video: https://www.youtube.com/watch?v=eDKcq_ND94g&t=609s
I then created different population sizes to prove the instability of small population sizes compared to large sizes. My small population that had more fluctuations and changes in allele frequency was 15 individuals. My large population which saw much less fluctuation than the small population contained 1000 individuals. After this I created a pie chart to show how the large population was much closer to the Hardy-Weinberg Equilibrium than the small population size. I then labeled these sheets "Population Sizes."
To test the effect of selection against homozygotes with the B allele, I copied the first generation of my initial small population model onto a new sheet labeled “Selection” and adjusted the function in the “BB” column for the number of each genotype to read =IF(E4="BB",1,0), programming Excel to place a 1 or 0 in the cells in this column whether or not a BB genotype was located in the corresponding zygote cell in order to put homozygotes for B at a disadvantage. I then multiplied this value by 0 in the lethal selection sheet and 0.5 in the partial selection sheet. After copying the gamete, zygote, and number for each genotype columns down to produce several hundred offspring to reduce instability of populations and ensure that only selection against the BB genotype was causing changes in the allele frequency, I copied the model to produce 5 generations and created the same graphs to consider the impact of selection against the BB genotype on the allele frequencies. These were done in populations of 1000.
I hypothesize that population sizes will have more fluctuation for allele frequencies in a small population rather than in a large population over multiple generations since allele frequencies should be more significantly altered by chance events in a small population than in a large population. I also believe that selection against homozygotes for one allele will decrease the frequency of that allele over multiple generations by reducing the number of organisms with that allele in the population and increasing the number of organisms without that allele frequency.
Materials:
I used Microsoft Excel on my surface to create the spreadsheets to model the Hardy-Weinberg Equilibrium
Methods:
To create the basic Excel spreadsheet to begin my experiment, I followed the steps from this video: https://www.youtube.com/watch?v=eDKcq_ND94g&t=609s
I then created different population sizes to prove the instability of small population sizes compared to large sizes. My small population that had more fluctuations and changes in allele frequency was 15 individuals. My large population which saw much less fluctuation than the small population contained 1000 individuals. After this I created a pie chart to show how the large population was much closer to the Hardy-Weinberg Equilibrium than the small population size. I then labeled these sheets "Population Sizes."
To test the effect of selection against homozygotes with the B allele, I copied the first generation of my initial small population model onto a new sheet labeled “Selection” and adjusted the function in the “BB” column for the number of each genotype to read =IF(E4="BB",1,0), programming Excel to place a 1 or 0 in the cells in this column whether or not a BB genotype was located in the corresponding zygote cell in order to put homozygotes for B at a disadvantage. I then multiplied this value by 0 in the lethal selection sheet and 0.5 in the partial selection sheet. After copying the gamete, zygote, and number for each genotype columns down to produce several hundred offspring to reduce instability of populations and ensure that only selection against the BB genotype was causing changes in the allele frequency, I copied the model to produce 5 generations and created the same graphs to consider the impact of selection against the BB genotype on the allele frequencies. These were done in populations of 1000.
Results:
My Microsoft Excel Spreadsheet:
My Microsoft Excel Spreadsheet:
https://onedrive.live.com/edit.aspx?cid=ae48a954d8d3cefb&page=view&resid=AE48A954D8D3CEFB!609&parId=AE48A954D8D3CEFB!101&app=Excel
Conclusion:
My model of small and large populations does support my hypothesis that different population sizes will cause a greater change in allele frequencies in a small population than in a large population over both one and multiple generations since chance events should have a greater impact on allele frequencies in a large population than in a small population.
My model also indicates that selection against B allele homozygotes does decrease the frequency of this allele and increase the frequency of the other allele by reducing the number of organisms with that allele in the population. Basically, as BB homozygotes decrease, AB and AA zygotes will increase. As a result, in later generations, AB zygotes will continue to decrease because they have the chance to produce BB zygotes which will die off.
I could have also tested different factors to change allele frequency such as mutation, disasters or extinctions, and an advantage for a certain allele frequency. For example, I could have favored heterozygotes by making them double in frequency. Through this experiment we were able to simulate populations to learn more about factors that change allele frequencies and zygotes. It gave us another look at evolution and how certain factors influence allele frequencies such as mutation, selection against a certain allele frequency, disasters/extinctions, and advantageous allele frequencies.
Conclusion:
My model of small and large populations does support my hypothesis that different population sizes will cause a greater change in allele frequencies in a small population than in a large population over both one and multiple generations since chance events should have a greater impact on allele frequencies in a large population than in a small population.
My model also indicates that selection against B allele homozygotes does decrease the frequency of this allele and increase the frequency of the other allele by reducing the number of organisms with that allele in the population. Basically, as BB homozygotes decrease, AB and AA zygotes will increase. As a result, in later generations, AB zygotes will continue to decrease because they have the chance to produce BB zygotes which will die off.
I could have also tested different factors to change allele frequency such as mutation, disasters or extinctions, and an advantage for a certain allele frequency. For example, I could have favored heterozygotes by making them double in frequency. Through this experiment we were able to simulate populations to learn more about factors that change allele frequencies and zygotes. It gave us another look at evolution and how certain factors influence allele frequencies such as mutation, selection against a certain allele frequency, disasters/extinctions, and advantageous allele frequencies.
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