Genetic limitations on models of specific interactions between a host and its parasite

摘要

Specific interaction between a resistance gene (Rgene) of the host and an avirulence gene (Agene) of the parasite is the basis of the gene-for-gene relationship.RandAgenes are conditional genes, capable of associating with either of two phenotypes depending on the presence or absence of the other. Although avirulence usually segregates as a dominant character, microevolutionary history suggests that in its primary function anAgene associates not with avirulence but with virulence, also thatR:Ainteraction generates a ldquo;stop signal,rdquo; which prevents disease development, and finally that the primary function of a recessivea-gene, when it replaces a dominantAgene, is one of negating the stop signal. Where several gene-for-gene relationships operate simultaneously, a singleR:Ainteraction is sufficient to prevent disease development.RandAgenes occupied inR:Ainteraction are thus epistatic over those which are not. Because of the characteristics of the gene-for-gene relationship, definite limitations are imposed on genetic study. In any genetic study there may be, because of these limitations, contributing genes in both the host and the parasite which are not detected.