Chapter 27, Problem 12EQ

A danger in computing heritability values from studies involving genetically related individuals is the possibility that these individuals share more similar environments than do unrelated individuals. In the experiment shown in Figure 28.8, which data are the most compelling evidence that ridge count is not caused by genetically related individuals sharing common environments? Explain.

Year	Mary’s Tomatoes	Hector’s Tomatoes
1	0.7	0.8
2	0.9	0.9
3	1.1	1.2
4	1.2	1.3
5	1.3	1.3
6	1.4	1.4
7	1.4	1.5
8	1.5	1.5
9	1.5	1.5
10	1.5	1.5
11	1.5	1.5
12	1.5	1.5

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?