Multi-allelic nature of the locus controlling leaf marking in subterranean clover

Abstract

The inheritance of leaf markings in subterranean clover (Trifolium subterraneum ssp. subterraneurn) was studied in diallel cross involving a parental genotype without a leaf marking and eleven others, each with a distinctive marking. The results indicate Mendelian inheritance, and each marking appeared to be controlled by a different allele at a single locus. An alternative interpretation of the segregation data might be that the leaf mark locus is complex and comprises many tightly linked genes. Four types of dominance were manifest in the heterozygous combinations, including one that has not previously been described. With the exception of a completely dominant allele, the dominance relationships among the other alleles could not be predicted. In one cross, the expression of one of the leaf mark alleles was partially modified, and this could be attributed to an independent recessive gene. Mutation appears to be the sole genetic mechanism by which new alleles arise. Their origin and evolution in subterranean clover is discussed with reference to Fisher's theory on the evolution of dominance.