The episome in an Hfr strain is inserted near the trp (tryptophan operon)locus.This Hfr strain is grown with an F^- Trp^- strain.From this mating, we isolate an F⁺ Trp⁺strain that can readily impart the Trp⁺ phenotype to F^- Trp^- strains, but no other traits are ever transferred.(When the original Hfr strain is mated with F⁻ strains, traits other than Trp⁺ can be transferred, although at lower frequency than Trp⁺. )What most likely has happened?

Question

Quizplus · Accepted Answer

The most likely explanation is that an F' plasmid containing the trp⁺ genes has been generated. This occurs when the episome (F factor) excises from the bacterial chromosome and includes some adjacent genes, in this case, the trp operon, allowing the transfer of these specific traits without transferring other traits.

The Episome in an Hfr Strain Is Inserted near the Trp