Other Mapping Designs

The granddaughter design is a variant of the half-sib design, widely used in dairy cattle QTL mapping. In this design, the half-sib family consists of the progeny-tested sons of an elite sire. The phenotype of the sons is given by the average production records of their daughters. This is a convenient design to implement because semen samples of the sire and his sons can be used as a source of DNA; semen samples of all progeny-tested sires in the United States are routinely collected in a special repository maintained by the U.S. Department of Agriculture (USDA) and made available to qualified scientists for QTL mapping. Progeny test data on the sire and his sons are also widely available through the USDA sire evaluation service. Backcross and F2 designs are implemented when mapping QTL responsible for trait differences between two populations that differ widely in trait value (such as broiler and layer chickens, disease-resistant and susceptible breeds of cattle). When the mapping population is very large and a large number of markers are followed, selective DNA pooling can reduce the genotyp-ing load ten- to one-hundredfold.

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