Heteroduplex heterozygotes in bacteriophage T4 involving mutations of various dimensions.

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Abstract
The DNA of an internal heterozygote contains different genetic information on opposite strands in a limited region of the molecule. True point mutations resulting from a base pair substitution will readily form internal heterozygotes during genetic recombination, but extended deletions will not, presumably because of distorted pairing between complementary strands of the DNA. The rH sign mutations of bacteriophage T4 arise from additions or deletions of small numbers of base pairs, and sometimes map as very small deletions. Sign mutants participate in internal heterozygotes at various characteristic frequencies which are measures of the extent of the mutational lesions. Criteria were developed for deciding whether mutants of any algebraic sign contain additions or deletions of base pairs. The DNA of internal heterozygotes encompassing sign mutations must contain very short single-stranded loop-outs.