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Problem box 9.2 answer

The difference between the homozygote marker class means is 30.7 - 26.4 = 4.3 cg so that a = 2.15 cg. Assuming that r = 0, a = 2.15 cg. Assuming instead that r = 0.2, then a = 2.15/ (1 - 2(0.2)) = 3.58 cg. The midpoint value is 26.4 + (30.7 - 26.4)/2 = 28.55 cg. The M1M2 marker class mean is less than the midpoint so d = 28.3 - 28.55 = -0.25. With r = 0.2, d = -0.25/(1 - 2(0.2))2 = -0.69. The coefficient of dominance is -0.25/2.15 = -0.12 if r = 0 and -0.69/3.58 = -0.19 if r = 0.2. The difference in seed weight between the Q1Q1 and Q2Q2 genotypes accounts for 4.3 cg/27 cg or 16% of the total seed weight difference between the two parental lines. The phenotypic effect is large enough to be considered a major gene.

Problem box 9.3 answer

The backcross design results in a = a - d and therefore is a biased estimate of the additive effect of a QTL unless there is no dominance (d = 0). See Table 9.8.

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