A large, genetically heterogeneous group of tomato plants was used as the original breeding stock by two different breeders, named Mary and Hector. Each breeder was given 50 seeds and began an artificial selection strategy, much like the one described in Figure 27.11. The seeds were planted, and the breeders selected the 10 plants with the highest mean tomato weights as the breeding stock for the next generation. This process was repeated over the course of 12 growing seasons, and the following data were obtained:

A. Explain these results.
B. Another tomato breeder, named Martin, got some seeds from Mary's and Hector's tomato strains (after 12 generations), grew the plants, and then crossed them to each other. The mean weight of the tomatoes in these hybrids was about 1.7 pounds. For a period of 5 years, Martin subjected these hybrids to the same experimental strategy that Mary and Hector had followed, and he obtained the following results:
Mean Weight of Tomatoes (pounds)
Year Martin's Tomatoes
1 .............................. 1.7
2 .............................. 1.8
3 .............................. 1.9
4 .............................. 2.0
5 .............................. 2.0
Explain Martin's data. Why was Martin able to obtain tomatoes heavier than 1.5 pounds, whereas Mary's and Hector's strains appeared to plateau at this weight?

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Mean Weight of Tomatoes (pounds) Mary's Tomatoes 0.7 0.9 1.1 1.2 1.3 1.4 1.4 1.5 1.5 1.5 1.5 1.5 Hector's Tomatoes 0.8 0.9 1.2 1.3 1.3 1.4 1.5 1.5 1.5 1.5 1.5 L.5 Year 7 10 12