- The purpose of this study was to isolate and characterize any
segregants of the heterogenotes formed from sexduction by an F'
donor. Following the mating of F' W4520, carrying an F' gal₁⁺
gal₂⁺ factor, with W3350, a gal₁⁻ gal₂⁻ recipient, a number of
recombinant clones were picked and examined for segregants.
From 5 such clones, 50 segregants of the gal⁺ phenotype and 50 of
the gal⁻ phenotype were isolated. The genotypes of these segregants
were determined as follows. The gal⁻ segregants were examined to
determine the genotype of any F factors carried, by crosses against
three gal⁻ recipient types, which were streptomycin resistant
mutants isolated early in the study. The failure of these segregants
to produce recombinants in these crosses was taken as evidence that
no F factors of the gal⁺ type were carried by these segregants. The
gal⁻ segregants were also analyzed for their chromosomal genotype by crosses against two gal⁻ F' homogenotes formed earlier in the
study. Again, failure of these crosses to produce gal⁺ recombinants
was noted and taken as evidence that these gal⁻ segregants carried
chromosomal genotypes of the gal₁⁻ gal₂⁻ type.
By a similar procedure, the 50 gal⁺ segregants were examined
to determine the genotype of any F factors carried, by crosses
against the same 3 gal⁻ recipient types, which in this case, were
azide resistant mutants isolated early in the study. The formation of
gal⁺ recombinants from these crosses was taken as evidence that
these 50 gal⁺ segregants carried F' factors of the type F gal₁⁺ gal₂⁺.
The segregants were cured of these F factors with acridine
orange and their chromosomal genotypes determined by crosses
against the same two gal⁻ F¹ homogenotes used earlier. The absence
of gal⁺ recombinant formation from these crosses confirmed that
these segregants carried chromosomes of the gal₁⁻ gal₂⁻ type.
It was found that no variation of genotype existed among the 50
segregants of each type. The 50 gal⁻ strains were concluded to be
either haploid parental types, with the genotype gal₁⁻ gal₂⁻ , resulting
from loss of the F factor in the sexductional heterogenotes, or
possibly homogenotes of the type gal₁⁻ gal₂⁻/ F gal₁⁻ gal₂⁻ , which
were undetectable in this system. The 50 gal⁺ segregants, carrying
the genotype gal₁⁻ gal₂⁻ / F gal₁⁺ gal₂⁺ , were of the same type as
the heterogenotes from which they were segregated. Since no recombinant types were found, it was concluded that the F' factors,
in this system, undergo recombination with their host chromosome,
during sexduction, at lower frequencies than expected from analogy
with transduction by bacteriophage.