Genetic analysis using trans-dominant linked markers in an F2 family

Trans-dominant linked markers pairs (trans referring to the repulsion linkage phase) provide a model for inferring the F2 progeny genotype based upon both the conditional probabilities of F2 genotypes, given the F2 phenotype, and prior information on marker arrangement. Prior information of marker arrangement can be readily obtained from a linkage analysis performed on marker segregation data in a family resulting by crossing the F1 individual to a "tester" parent or else can be obtained directly from the gametes of the F1, or from recombinant inbred lines. We showed that a trans-dominant linked marker (TDLM) pair can be recoded as a "co-dominant megalocus" when the recombination fraction, r1, for apair of TDLMs is less than 0.05. We obtained a maximum-likelihood estimator (MLE) of the recombination frequency, r2, between a TDLM pair and a co-dominant marker in an F2 family using the EM algorithm. The MLE was biased. Mean bias increased as r1 and r2 increased, and decreased as sample size increased. The information content for r2 was compared to the information content of dominant and co-dominant markers segregating in an F2 family. It was almost identical with two co-dominant markers when r1≤0.01 and r2≥0.05. For larger values of r1, (0.05≤r1≤0.15) a TDLM pair provided 75%-66% of the information content of two co-dominant markers. Although dominant markers can be converted to co-dominant markers by a laborious process of cloning, sequencing, and PCR, TDLM pairs could easily substitute for co-dominant markers in order to detect quantitative trait loci (QTLs) and estimate gene action in an F2 family.