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SUMMARY: Wild-type Streptomyces coelicolora 3(2), and many mutant and recombinant derivatives of it, are of the if (Initial Fertility) type. At an early step in the production of recombinant strains from some of the first derivatives of a3 (2), a variant fertility type arose (nf: Normal Fertility), and subsequently if and nf segregated within the pedigree of stock cultures. if x if crosses are about 100-fold less fertile than nf x nf or if x nf crosses, but the clearest distinction between if and nf is achieved by crossing with a strain of the previously described uf (Ultra-Fertile) type, when the difference in fertility approaches 1000-fold.The if strains give rise to uf strains with a high spontaneous frequency, and the frequency is increased by ultraviolet or X-irradiation but not appreciably by N-methyl-N'-nitro-N-nitrosoguanidine. nf strains do not give rise to uf variants with a high frequency.The difference between if and nf is determined by a chromosomal locus near the 9 o'clock position on the linkage map. There is no evidence for the infectious conversion of one type of strain to the other in a mixed culture.In crosses with an nf strain, both if and uf strains contribute the whole chromosome to the effective merozygotes, and the nf strain contributes the fragment, which obligatorily includes the 9 o'clock region. However, whereas in uf x nf crosses there is obligate inheritance of the 9 o'clock region of the nf genome by all sexually produced progeny, this is not true of if x nf crosses.

Genetic Control of Fertility in Streptomyces coelicolor A3(2): the IF Fertility Type