Angela A. Garibaldi Week 2

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Evolution Aipotu IV

Note: Protocol adapted from Molecular Genetics Explorer Evolution Aipotu IV protocol

Methods and Results

Select for Red

  1. Click on the Red organism in the Greenhouse to select it; its border will turn green. While holding the shift key, click on the White organism in the Greenhouse to add both
  2. Click the Load button in the Controls to load the World with a roughly 50:50 mix of red and white organisms.Note: Resulting mix was 58 white, 42 red organisms.
  3. Set the Fitness settings in the Settings panel to select for red. Set the fitness of red to 10(the maximum) and all the other colors to 0 (the minimum).
  4. Prediction: I predict that due to the increase in fitness of the red, and the 0 fitness of other colors (including white), the next few generations should see a decrease in all colors that are not red. Eventually future generations will be all red.
  5. Test: Click the One Generation Only button in the Controls. This will run one generation only. First, the starting flowers will contribute to the gene pool based on their fitnesses. Then the starting flowers will die off and be replaced by exactly 100 offspring. Each offspring flower will get two alleles randomly chosen from the gene pool.
  6. Result:The red count after one generation jumped to 80, whereas the white count dropped to 20. Overall red is increasing rapidly over generations. It takes about 9 generations to get pure red. Some all red generations can have white offspring because two heterozygotes (one recessive white allele, one dominant red allele) may have produced a homozygous offspring with two recessive white alleles.


Select for White

  1. Click on the Red organism in the Greenhouse to select it; its border will turn green. While holding the shift key, click on the White organism in the Greenhouse to choose both.
  2. Click the Load button in the Controls to fill the World with a roughly 50:50 mix of red and white organisms. Note: Resulting mix was 50 white and 50 red organisms.
  3. Set the Fitness settings in the Settings panel to select for white. Set the fitness of white to 10 (the maximum) and all the other colors to 0 (the minimum).
  4. Prediction: With the fitness of white increased and all other colors set to 0, the number of red flowers will slowly decline over time. At first the white count will hold constant until red homozygotes are eliminated.As more heterozygotes produce offspring, the white count will increase in numbers and eventually the population over a longer period of time than the red selected scenario will become all white.
  5. Test: Click the One Generation Only button in the Controls. This will run one generation only. First, the starting flowers will contribute to the gene pool based on their fitnesses. Then the starting flowers will die off and be replaced by exactly 100 offspring. Each offspring flower will get two alleles randomly chosen from the gene pool.
  6. Result:My prediction was false; it took only one generation to become completely white.
  7. Question:Why does it take more generations to get to pure red than it does to get to pure white?
  • Response: It takes longer to get pure red in that an organism can still be red, yet carry the white allele, and therefore will still survive and have fitness when selecting for red organisms. But, this means that future generations can still produce white offspring on occasion when two heterozygotes produce offspring. On the contrary, when selecting for white, an organism cannot be white and carry a red allele because in order to be white, an organism must be homozygous because the white allele is recessive and the red allele is dominant. Therefore, if all plants with even one red allele must be red, then all organisms carrying a red allele must also have 0 fitness and will not continue on to the next generation.

Quantitative: Hardy-Weinberg Equilibrium & Natural Selection

  1. Load the World with only the Red organism from the Greenhouse. The World should be entirely red.
  2. Show the colors of both alleles in each organism by checking the Show colors of both alleles in the World Settings part of the Preferences. You should see little red and white rectangles in the upper left corner of each organism in the World – this indicates that each has one red and one white allele = genotype Rr.
  3. Set all Fitnesses to 5.
  4. Result:The population is at Hardy-Weinberg Equilibrium based on the following calculations and reasoning:
Allele frequencies in the starting population:

Genotype Number           #R’s               #r’s
RR 27                     54                    0
Rr 51                     51                   51
rr 22                      0                   44
TOTAL:                    105                  95
frequency of R (p)=105/200=0.525
frequency of r (q)=95/200=0.475

Genotype frequencies expected at HWE:

frequency of RR = p2 =(.475)^2 (100)=22.56
frequency of Rr = 2pq =2(.525)(.475)(100)=49.88
frequency of rr = q2 =(.525)^2(100)=27.56

The population is at Hardy-Weinberg Equilibrium because the frequencies of p and q add up to 1 and the frequencies translated into number of individuals of RR, Rr, and rr equate to the original population.

Part II

  1. Run one generation only. Is that population at HWE? Result: The population is still HWE.
  2. Set the Fitness settings in the Settings panel to select for red. Set the fitness of red to 10(the maximum) and all the other colors to 0 (the minimum).
  3. Prediction:After several generations of this selection, p and q should still equal 1 although the frequencies of each may distribute differently based on which alleles are being selected for. In this case, if p represents the R allele and q represents the r allele, then p should increase overall and r will probably decrease.
  4. Test: Click the One Generation Only button in the Controls. Do this a few times.
  5. Result:
Genotype Number         #R’s          #r’s
RR 65                    130             0
Rr 30                     30            30
rr 5                       0            10
TOTAL:                   160            40

frequency of R (p) = 160/200= 0.8
frequency of r (q) = 40/200= 0.2

This result matches my prediction. The frequencies of p and q still add up to 1 and the frequency of p increased as that allele is being selected for. The allele being selected against (q) decreased.


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