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which after simplifying the rightmost term gives

This equation is then simplified by factoring out d, multiplying through, and adding terms to obtain the expression

A numerical example will help to illustrate the marker class phenotypic mean values and how they result in estimates of a and O. Different breeds of dog exhibit a very wide range of body sizes. An allele of the insulin-like growth factor l gene (IGFl) has been shown to be frequent in small dog breeds (<9 kg) but to have a frequency of near zero in large dog breeds (>30 kg; Sutter et al. 2007). Therefore, the IGFl locus is likely to be a major gene (a QTL that explains a large amount of quantitative trait variation) for body size in dogs. Let's assume there are two IGFl alleles segregating within a single randomly mating population of dogs and that body size ranges between a minimum of 9 kg and a maximum of 30 kg (see Fig. l0.l).

Imagine that an F2 QTL mapping design was carried out along the lines of Fig. 9.15 using large (30 kg) and small (9 kg) dogs as the Pl individuals. Suppose that the marker class means were GM M = 20 kg, Gmim2 = 18 kg, and Gm2m2 = 12 kg. Also, make the unrealistic assumption for the moment that there is no recombination between the QTL and the marker locus (r = 0). The observed value of 2a is the difference between G

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