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biology end of course orq

Biology End of Course ORQ



Researchers conducted a 20-generation, artificial selection experiment to modify the oil content of corn. They cross-pollinated specific corn plants and measured the increase of oil content in the offspring. In the resulting generations they only allowed the plants with the highest oil content to be pollinated. They compared their results to corn plants that were allowed to pollinate randomly. The results of the artificially bred corn are presented in this graph.

part a identify the parts of the experiment
Part A: Identify the Parts of the Experiment
    • Independent Variable = selective breeding of corn plants over 20 generations (which plants are allowed to breed each generation)
    • The Independent Variable is the cause that is purposely being changed/manipulated
  • Dependent Variable = oil content of the corn
    • The Dependent Variable is the effect that is being measured
  • Experimental Group = cross-pollinated plants
    • The Experimental Group is the group that gets the changed independent variable
  • Control Group = randomly pollinated plants
    • The Control Group is the group that does NOT get the changed independent variable (normal conditions) and is used for comparison of the results
part b artificial vs natural selection
Part B: Artificial vs. Natural Selection
  • Artificial Selection = also known as selective breeding; humans manipulate the gene pool and select which phenotypes are desired and only allow organisms with those characteristics to breed and produce offspring
  • Natural Selection = nature determines which phenotypes are beneficial for survival &/or reproduction; some phenotypes are more advantageous while others put the organism at a disadvantage; the traits that allow organisms to better leave genes in the next generation are amplified in the gene pool in subsequent generations; over time, there is a shift in the allele frequency in the population toward the more advantageous phenotypes
part c type of natural selection
Part C: Type of Natural Selection
  • Disruptive selection = both extreme phenotypes are more beneficial than the intermediate phenotypes so the intermediates are eliminated from the gene pool
  • Stabilizing = intermediate phenotypes are more beneficial than extreme phenotypes so the extremes are eliminated from the gene pool
  • Directional = there is a shift in the allele frequency of the gene pool towards one specific phenotype which becomes more pronounced over several generations
  • This is not disruptive or stabilizing because oil content is constantly increasing throughout the generations SO the gene pool is shifting in one direction. This is directional selection. Having higher oil content is more desirable in the experiment it is being selected for breeding (only the plants with the highest oil content are allowed to breed). Lower oil content is less desirable so it is selected against (those plants are not allowed to breed).
part d predict the results in 5 generations
Part D: Predict the Results in 5 Generations
  • At generation 25, the oil content of the corn should be approximately 12.5% if the trend continues.
  • According to the graph, the oil content starts at 5% in generation 0 and increases to 11% in generation 20. That is an overall increase of 6%.
  • If you find the rate of increase (slope) by dividing 6% by 20 (the number of generations). That is an increase of 0.3% each generation.
  • If this trend continues, the oil content would increase by 1.5% over 5 generations (0.3%*5 generations).
  • Add 1.5 to 11 (last recorded oil content; generation 20) which gives an oil content of 12.5% in generation 25