1. Ashley Vander Sys
BIOLOGY Dr. Kristina Ernest & Izak Neziri
EVOLUTION BY ARTIFICIAL
SELECTION IN BRASSICA RAPA

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Ashley N. Vander Sys
Evolution by Artificial Selection in Brassica rapa
Biology 181, Dr. Kristina Ernest, TA: Izak Neziri
November 18, 2015
INTRODUCTION
Study Question: Can the number of trichomes be increased in Brassica rapa through artificial selection?
Null Hypothesis: The number of trichomes for proceeding generations is not heritable.
Null Hypothesis Prediction: The number of trichomes for the offspring of our control and hairiest plants
will show little to no variation in their number of trichomes.
Alternative Hypothesis: The number of trichomes for the proceeding generations is heritable.
Alternative Hypothesis Prediction: The number of trichomes for the offspring of our control and hairiest
plants will vary, with hairiest offspring having more trichomes.
METHODS
In September 2015, we were placed in groups of 4 and picked out 3 Brassica rapa plants each (12
for our group) at random in the CWU Greenhouse. We then took our 12 plants back to the classroom and
counted the total number of trichomes on the petiole of the 1st
true leaf of each plant in our sample using a
hand lens (Figure 1).

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Figure 1: Diagram of our standards in counting the trichomes on the petiole of the 1st true leaf of each Brassica rapa plant.
Overall our class counted the trichomes of 72 Brassica rapa. We then used the random number
generator in Excel to pick for 15 plants at random. These 15 plants were then put aside as our controls.
After compiling the class data and setting aside our controls we choose the 15 hairiest plants of our
remaining 57 plants. These were put aside along with the control group, while remaining separate from
each other. When the Brassica rapa started to flower the TAs pollinated them with Q-tips. The controls
were pollinated together. The hairiest were pollinated together. Both groups were kept separate. Plants
were kept in the Greenhouse in a pot size of 5 cm2
individually throughout the duration of their cycles.
Seeds were collected after 7 weeks. If our plants had lived however,we would have next counted the
trichomes of the proceeding generation. However, they did not survive, so we are applying data collected
in 2013 from CWU for the rest of this report. Chi-square tests will be used to determine if the number of
trichomes in the following generations is a heritable trait by testing for relatively between the observed
number of trichomes in Generation 2 of our control and hairy Brassica rapa groups and the calculated
expected number of trichomes (expected number of trichomes is a calculation based on what would be the

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expected number of trichomes in the offspring if Brassica rapa are pollinated under non-controlled
conditions).
RESULTS
Our results showed that when hairy Brassica rapa was breed with other hairy Brassica rapa,the
offspring had an overall higher output of trichomes per plant in comparison to the 2nd
Generation in the
control group. The chi-square test showed that the difference between the calculated expected number of
trichomes in generation 2 and the observed trichomes in generation 2 of our hairy Brassica rapa
population were significantly different, therefore suggesting trichomes are a heritable trait and can result
from artificial selection (Table 1, Table 2). In contrast,the control chi-square test was not statistically
significant as it just suggested that the number of trichomes observed in the control generation 2
population was closely comparable and relatable to the calculated expected number of trichomes. The
strong miscorrelation between the hairy Brassica rapa chi-square test result (Chi-square = 15.086, df=5,
=0.01) and the strong correlation between the control group and the calculated expected number of
trichomes in Generation 2, would suggest trichomes are heritable. Therefore,we reject our null
hypothesis and accept our alternative hypothesis that trichomes are a heritable trait.
CHI-SQUARE TESTS FOR GENERATION 2 AND EXPECTED GENERATION
Table 1: Chi-square Test for the Trichomes in the Hairy Generation 2 Plants
HAIRY
Trichomes Gen 2 Hairy Observed ExpectednumberinGen2 O-E (O-E)^2 (OE)^2/E
0 to 3 18 41 -23 529 12.90244
4 to 6 11 5 6 36 7.2
7 to 9 8 4 4 16 4
10 to 12 11 7 4 16 2.285714
13 to 15 5 4 1 1 0.25
16+ 16 9 7 49 5.444444
Total 32.0826

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Table 2: Chi-square Test for the Trichomes in the Control Generation 2 Plants
CONTROL
Trichomes Gen 2 Control Observed ExpectednumberinGen 2 O-E (O-E)^2 (OE)^2/E
0 to 3 49 41 8 64 1.560976
4 to 6 4 5 -1 1 0.2
7 to 9 5 4 1 1 0.25
10 to 12 4 7 -3 9 1.285714
13 to 15 2 4 -2 4 1
16+ 8 9 -1 1 0.111111
Total 4.407801
Table 3: Chi-square Test and Expected Calculations for Generation 2
EXPECTED
Trichomes Gen 1 Observed ExpectednumberinGen2 O-E (O-E)^2 (O-E)^2/E
0 to 3 43 41 2 4 0.097560976
4 to 6 5 5 0 0 0
7 to 9 4 4 0 0 0
10 to 12 7 7 0 0 0
13 to 15 4 4 0 0 0
16+ 9 9 0 0 0
Total 0.097560976
By observing the number of trichomes in hairy plants to control plants (column 2) in Table 1 and
Table 2 we were able to back up our chi-square test results. We also calculated the average trichomes for
Generation 2 in the Hairy, Control and Expected groups individually (Table 4, Table 5, Table 6). An
overall higher average was calculated for our hairy Brassica rapa group than compared to the control and
expected groups, with an average of 8.6 trichomes per individual plant (Table 4). The control average was
4.6 trichomes per individual plant (Table 5) and the expected average was 5.7 trichomes per plant (Table
6).
CALCULATED AVERAGES OF TRICHOMES FOR EACHPOPULATIONINGENERATION 2

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Table 4: Calculated Trichome Average for Generation 2 of the Hairy Brassica rapa Population
Hairy Average
Trichome Category Gen 2 Hairy Observed Average per Category Total
0 to 3 18 1.5 27
4 to 6 11 5 55
7 to 9 8 8 64
10 to 12 11 11 121
13 to 15 5 14 70
16+ 16 16 256
Generation 2 Hairy Average 8.594202899
Table 5: Calculated Trichome Average for Generation 2 of the Control Brassica rapa Population
Control Average
Trichome Category Gen 2 Control Observed Average per Category Total
0 to 3 49 1.5 73.5
4 to 6 4 5 20
7 to 9 5 8 40
10 to 12 4 11 44
13 to 15 2 14 28
16+ 8 16 128
Generation 2 Control Average 4.631944444
Table 6: Calculated Average of Trichomes for Expected Generation 2
Expected Average
Trichome Category Expected Number in Gen 2 Average per Category Total
0 to 3 41 1.5 61.5
4 to 6 5 5 25
7 to 9 4 8 32
10 to 12 7 11 77
13 to 15 4 14 56
16+ 9 16 144
Generation 2 Expected Average 5.65

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Figure 2: Frequency Histogram of trichome numbers for the entire Brassica rapa population. Pooled data from 72 plants from
CWU greenhouse, February 2013.
CONCLUSION
Based on the results from our chi-square test of hairy Brassica rapa (Chi-square =
32.0826) and the control Brassica rapa group (Chi-square = 4.407801) we reject our null
hypothesis that trichomes are not heritable and accept our alternative hypothesis that trichomes
are heritable. As we predicted in our Alternative Hypothesis Prediction, the number of trichomes
in our hairy population were higher than that in the control. We can also safely reject the null
hypothesis with the addition of the average trichome number for each population showing favor
for our alternative hypothesis. As briefly explained in the results section, the Chi-square result of
32.0826 for our hairy Brassica rapa group suggest that the observed number of trichomes for our
generation 2 in the hairy group are highly uncorrelated with the expected number of trichomes
we calculated. Meaning that trichomes, when artificially selected, are drastically different than if
they were breed under uncontrolled circumstances. In comparison to the Chi-square result of
4.407 for our control group that suggests that the number of trichomes for our control group

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closely match the expected number of trichomes. This result suggests that when Brassica rapa
are breed under normal parameters the variation of trichome numbers per plant is relatively
stable and unchanged. As stated in the result section, the average number of trichomes per each
group also shows support of my alternative hypothesis. The calculated average for trichomes in
all the Generation 2 hairy plants were 8.6 in comparison to the average of the control which was
4.63 trichomes per plant in Generation 2 of our control group. This suggests that on average, the
offspring of the hairy Brassica rapa had more trichomes per plant than those in the control
group. Considering each group was cross-breed with Brassica rapa plants similar in trichome
numbers, this further suggests that trichomes are a heritable trait and are applicable under
artificial selection standards.