Download Biology End of Course ORQ

Biology End of Course ORQ
GET OUT YOUR OPEN RESPONSE!
Question
Researchers conducted a 20generation, artificial selection
experiment to modify the oil
content of corn. They crosspollinated 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
• 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
• 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
• 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
• 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