MUTATIONAL HETEROZYGOTES IN BACTERIOPHAGES

Abstract
When bacteria infected with T2 or T4 bacteriophages are exposed to the mutagen 5-bromodeoxyuridine, some of the resultant mutant phages are heterozygous, giving rise to mixed clones of mutant and nonmutant progeny. The proportion of heterozygotes among mutants rises to at least 80% when progeny phages are harvested very shortly after addition of the mutagen. This proportion is reduced by prolonged exposure of the infected bacteria to 5-bromodeoxyuridine. These findings are interpreted to mean that the mutational heterozygosity of a phage particle resides in a double stranded deoxyribonucleic acid (DNA) molecule which contains one mutant and one nonmutant polynucleotide chain.