A simple method for estimating recombination percentages and linkage intensities from F2 data: examples from Triticum monococcum and other self-fertilizing diploid plant species

We offer an alternative approach to the extensively used maximum likelihood and product methods for calculating recombination values and linkage intensities from F2 data. This new method which we designate as the square root approach is simpler than the ones in current use in that it obviates the need for formulae and tables. It can be applied to autosomal F2 data from F1's heterozygous in both the coupling and repulsion phases. It has greater applicability than the product method in that it can be used in all cases involving 2-, 3-, 4-, 6- and 9-class segregations regardless whether gene interaction occurs or not, provided the double recessive and other specific phenotypes are each determined by one particular genotype. The proposed method is based on the same well established genetic facts as the other two approaches. Percent recombinant gametes and therefore percent recombination are calculated by deriving the square root of the proportion of the F2 population that expresses the double recessive or equivalent phenotype. The recombination values obtained by our method are compared with those derived by product method for 17 crosses in 7 different species and were found to be insignificantly different from the latter. The advantages and disadvantages of the square root method compared with the two most used ones are discussed.