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Course: Biology library > Unit 26

Lesson 2: Artificial selection
Science
Biology library
More about evolution and natural selection
Artificial selection
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Artificial selection

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Problem

Brassica rapa plants have small, hair-like structures called trichomes on their stems and leaves. The number of trichomes on a plant is genetically determined and can vary widely among individuals.
A group of students grew a population of B. rapa plants, Generation 1, in their classroom and counted the number of trichomes on the first true leaf of each plant (Figure 1).
A bar graph with Number of plants on the y-axis and Trichome number on the x-axis. The columns of data are as follows: column 5, 50 plants; column 10, 20 plants; column 15, 25 plants; column 20, 12 plants; column 25, 8 plants; column 30, 6 plants; column 35, 3 plants; column 40, 3 plants; column 45, 1 plant; column 50, 1 plant.
Figure 1: Trichome number distribution for Generation 1 B. rapa plants.
Next, the students used the Generation 1 plants with the highest number of trichomes as parents for the next generation, Generation 2. The students grew the B. rapa plants of Generation 2 and counted the number of trichomes on the first true leaf of each plant (Figure 2).
A bar graph with Number of plants on the y-axis and Trichome number on the x-axis. The columns of data are as follows: column 5, 7 plants; column 10, 6 plants; column 15, 17 plants; column 20, 19 plants; column 25, 23 plants; column 30, 6 plants; column 35, 7 plants; column 40, 4 plants; column 45, 2 plants; column 50, 0 plants.
Figure 2: Trichome number distribution for Generation 2 B. rapa plants.
Then, the students used the Generation 2 plants with the highest number of trichomes as parents for the third generation, Generation 3.
Which of the following graphs best predicts the distribution of trichome number in Generation 3?
Choose 1 answer: