FLOWERING PLANT SELF-INCOMPATIBILITY - THE MOLECULAR POPULATION-GENETICS OF BRASSICA S-LOCI

Self-incompatibility systems in different angiosperm families are revi ewed, and the evidence that incompatibility has arisen several times i s outlined. New data on the sequence polymorphism of self-incompatibil ity loci from two different angiosperm families are compared with resu lts from other highly polymorphic loci, particularly MHC loci. We disc uss what molecular genetic analyses of these sequences can tell us abo ut the nature and maintenance of the polymorphism at self-incompatibil ity loci. We suggest that there is evidence for recombination at the B rassica self-incompatibility loci, so that it may be possible to disce rn regions that are particularly functionally important in the recogni tion reaction, even though the long-term maintenance of polymorphisms in these amino acid residues has caused the evolution of many other se quence differences between alleles.