Multi‐allelic self‐incompatibility polymorphisms in plants

The multi‐allelic self‐incompatibility polymorphisms in angiosperms have long interested geneticists and population geneticists, but the limits of classical genetic resolution were reached many years ago. In recent years, new progress has been made by molecular genetic approaches. Intriguing similarities to and differences from the fungal systems are emerging. The polymorphism at these loci is now known to be even more baroque than appeared from classical genetic studies. Alleles differ so much at the level of both the DNA and protein sequence that they would be difficult to recognise as products of the same locus, were it not for the presence of certain conserved regions. Despite the successes of the recent work, the locus responsible for the specificity of the incompatibility reaction in pollen, and the mechanism of self‐incompatibility, remain elusive.