AbstractThe widespread occurrence of genetic circularity suggests a selective advantage to map circularityper se.Circularity permits gene clustering relations not possible in linear maps; that is, every gene in a circular map can have two nearest map neighbors, two next nearest, etc. It seems possible that map circularity is a consequence of the selective forces responsible for the clustering of genes of related function. Certain features of the pattern of crossing‐over in various fungi suggest that circularity of linkage maps is there to be found. A concurrence of high frequencies of second‐division segregation and negative chromatid interference across the centromere, both of which phenomena have been reported, is a feature of a simple hypothetical crossover pattern that generates circular linkage m