Predicting parental genotypes and gene segregation for tetrasomic inheritance

Recent genome mapping projects in tetraploid plant species require a method for analysing the segregation patterns of molecular marker loci in these s pecies. The present study presents a theoretical model and a statistical an alysis for predicting the genotypes of a pair of tetraploid parents at a co dominant (for example, RFLPs, microsatellites) or dominant (for example, AF LPs, RAPDs) molecular marker locus based on their and their progeny's pheno types scored at that locus (gel-band patterns). The theory allows for null alleles and for any degree of double-reduction to be modelled. A simulation study was performed to investigate the properties of the theoretical model . This showed that in many circumstances both the parental genotypes can be correctly identified with a probability of nearly 1, even when the molecul ar data were complicated by null alleles or double-reduction. Configuration s where the parental genotype cannot be identified are discussed. The power to detect double-reduction varies considerably, depending on the proportio n of identical alleles carried and shared by the parents, and the number of null alleles. Incorrect deductions of the occurrence of double-reduction w ere rare. The method was applied to data on a microsatellite locus segregat ing in the parents and 74 offspring of a tetraploid potato cross. Twentyfou r parental configurations were consistent with the parental gel pattern, bu t only one of these was compatible with all the phenotypic data on the offs pring. The feasibility for extending the present model to predict segregati on of several linked loci, and particularly the linkage phase, is briefly d iscussed.