What is self incompatibility in gametophyte and sporophyte ?
In gametophytic self-incompatibility (GSI), the SI phenotype of the pollen is determined by its own gametophytic haploid genotype. This is the more common type of SI. Two different mechanisms of GSI have been described in detail at the molecular level, and their description follows.Sporophytic self-incompatibility (SSI)
In sporophytic self-incompatibility (SSI), the SI phenotype of the pollen is determined by the diploid genotype of the anther (the sporophyte) in which it was created. This form of SI was identified in the families: Brassicaceae, Asteraceae, Convolvulaceae, Betulaceae, Caryophyllaceae, Sterculiaceae and Polemoniaceae.Up to this day, only one mechanism of SSI has been described in detail at the molecular level, in Brassica(Brassicaceae).
Since SSI is determined by a diploid genotype, the pollen and pistil each express the translation products of two different alleles, i.e. two male and two female determinants. Dominance relationships often exist between pairs of alleles, resulting in complicated patterns of compatibility/self-incompatibility. These dominance relationships also allow the generation of individuals homozygous for a recessive S allele.
Compared to a population in which all S alleles are co-dominant, the presence of dominance relationships in the population, raises the chances of compatible mating between individuals. The frequency ratio between recessive and dominant S alleles, reflects a dynamic balance between reproduction assurance (favoured by recessive alleles) and avoidance of selfing (favoured by dominant alleles).[