Segregation Models for Disomic, Tetrasomic and Intermediate Inheritance in Tetraploids: A General Procedure Applied to Rorippa (Yellow Cress) Microsatellite Data

摘要

Tetraploid inheritance has two extremes: disomic in allotetraploids and tetrasomic in autotetraploids. Thenpossibility of mixed, or intermediate, inheritance models has generally been neglected. These could wellnapply to newly formed hybrids or to diploidizing (auto)tetraploids. We present a simple likelihood-basednapproach that is able to incorporate disomic, tetrasomic, and intermediate inheritance models and estimatesnthe double-reduction rate. Our model shows that inheritance of microsatellite markers in natural tetraploidsnof Rorippa amphibia and R. sylvestris is tetrasomic, confirming their autotetraploid origin. However, in F1nhybrids inheritance was intermediate to disomic and tetrasomic inheritance. Apparently, in meiosis,nchromosomes paired preferentially with the homolog from the same parental species, but not strictly so.nDetected double-reduction rates were low.We tested the general applicability of our model, using publishednsegregation data. In two cases, an intermediate inheritance model gave a better fit to the data than thentetrasomic model advocated by the authors. The existence of inheritance intermediate to disomic andntetrasomic has important implications for linkage mapping and population genetics and hence breedingnprograms of tetraploids. Methods that have been developed for either disomic or tetrasomic tetraploids maynnot be generally applicable, particularly in systems where hybridization is common.