Recombination between mutants of Phycomyces with abnormal phototropism

Sexual crosses were studied between mutants of Phycomyces blakesleeanus with abnormal phototropism (phenotype mad). Recombination frequencies were determined among five genes madA to madE. No clear evidence was found for linkage between any of the genes. Inconsistent results in crosses involving madC are attributed to nonisogenicity between the particular strains used. One mad strain was discovered to be a double mutant. A new gene, tentatively designated madG, was segregated from a cross involving that strain.