Statistical aspects of genetic mapping in autopolyploids

Many plant species of agriculture importance are polyploid, having more tha n two copies of each chromosome per cell. In this paper, we describe statis tical methods for genetic map construction in autopolyploid species with pa rticular reference to the use of molecular markers. The first step is to de termine the dosage of each DNA fragment (electrophoretic band) from its seg regation ratio. Fragments present in a single dose can be used to construct framework maps for individual chromosomes. Fragments present in multiple d oses can often be used to link the: single chromosome maps into homologous groups and provide additional ordering information. Marker phenotype probab ilities were calculated for pairs of markers arranged in different configur ations among the homologous chromosomes. These probabilities were used to c ompute a maximum likelihood estimator of the recombination fraction between pairs of markers. A likelihood ratio test for linkage of multidose markers was derived. The information provided by each configuration and power and sample size considerations are also discussed. A set of 294 RFLP markers sc ored on 90 plants of the species Saccharum spontaneum L. was used to illust rate the construction of an autopolyploid map. Previous studies conducted o n the same data revealed that this species of sugar cane is an autooctaploi d with 64 chromosomes arranged into eight homologous groups. The methodolog y described permitted consolidation of 54 linkage groups into ten homologou s groups. (C) 1999 Elsevier Science B.V. All rights reserved.