NON-MENDELIAN TRANSMISSION OF APOMIXIS IN MAIZE-TRIPSACUM HYBRIDS CAUSED BY A TRANSMISSION RATIO DISTORTION

Apomixis is a mode of asexual reproduction through seeds. The apomicti c process bypasses both meiosis and egg cell fertilization: producing offspring that are exact genetic replicas of the mother plant. In the Tripsacum agamic complex, all polyploids reproduce through the diplosp orous type of apomixis, and diploids are sexual. In this paper, molecu lar markers linked with diplospory were used to analyse various genera tions of maize-Tripsacum hybrids and backcross derivatives and to deri ve a model for the inheritance of diplosporous reproduction. The resul ts suggest that the gene or genes controlling apomixis in Tripsacum ar e linked with a segregation distorter-type system promoting the elimin ation of the apomixis alleles when transmitted through haploid gametes . Hence, this model offers an explanation of the relationship between apomixis and polyploidy. The evolutionary importance of this mechanism , which protects the diploid level from being invaded by apomixis, is discussed.