Estimation of linkage in trisomic inheritance.

Based on F2 families derived from selfed F1 trisomic plants we have developed a genetic model to estimate linkage relationships between pairs of loci located on the extra chromosome. Genotypic frequencies of each class expected in a trisomic F2 family have been calculated and the maximum-likelihood equations for recombination-fraction estimation have been derived for a variety of genetic situations. Morton's test of homogeneity was used to compare recombination fractions estimated between loci exhibiting trisomic segregation to those obtained in families where the same loci showed Mendelian segregation. This method has been applied to an analysis of morphological, isozyme and RAPD data from faba bean (Vicia faba L.).