marker-assisted selection in wheat - ictsd

Chapter 12 – Marker-assisted selection in dairy cattle 207Figure 3The granddaughter designMAmaMA??ma??The grandsire is assumed to be heterozygous for a QTL and a linked genetic marker. As in Figure 2, only a single familyis shown. The two alleles of the marker locus are denote “M” and “m”, and the two alleles of the QTL are denoted “A”and “a”. Alleles of maternal origin are denoted by question marks. Genotypes are not listed for the granddaughtersbecause they were not genotyped.tive frequencies. To answer this question,Weller et al. (2002) proposed the “modifiedgranddaughter design” presented inFigure 4. Assume that a segregating QTLfor a trait of interest has been detectedand mapped to a short chromosomalsegment using either a daughter or a granddaughterdesign. Consider the maternalgranddaughters of a grandsire with a significantcontrast between his two paternalalleles. This grandsire will be denoted the“heterozygous grandsire”. Each maternalgranddaughter will receive one allele fromher sire, who is assumed to be unrelated tothe heterozygous grandsire, and one allelefrom her dam, who is a daughter of theheterozygous grandsire. Of these granddaughters,one-quarter should receive thegrandpaternal QTL allele with the positiveeffect, one-quarter should receive the