Question

You are provided with cultures with the following characteristics:
Culture 1: F⁺, genotype A⁺B⁺C⁺
Culture 2: F ̄, genotype A ̄B ̄C ̄
a. Indicate the possible genotypes of a recombinant cell resulting from the conjugation of cultures 1 and 2.
b. Indicate the possible genotypes of a recombinant cell resulting from conjugation of the two cultures after the F⁺ has become an Hfr cell.

Accepted Answer

Step 1: Understand the genotypes and mating types of the two cultures. Culture 1 is F^+ with genotype A^+B^+C^+, meaning it carries the fertility factor (F plasmid) and has wild-type alleles for genes A, B, and C. Culture 2 is F^-, with genotype ĀB̄C̄, meaning it lacks the F plasmid and has mutant alleles for these genes. Step 2: For part (a), during conjugation between an F^+ donor and an F^- recipient, the F plasmid is transferred from the donor to the recipient. Since the F plasmid is separate from the bacterial chromosome, only the F plasmid genes (and possibly some plasmid genes) are transferred, not the chromosomal genes A, B, and C. Therefore, the recombinant F^- recipient will gain the F plasmid and become F^+, but its chromosomal genotype remains ĀB̄C̄. Step 3: For part (b), when the F^+ plasmid integrates into the donor's chromosome, the cell becomes an Hfr (high frequency recombination) strain. During conjugation, the Hfr cell transfers part of its chromosomal DNA starting from the integrated F factor into the F^- recipient. This can result in recombinants with new combinations of alleles for genes A, B, and C depending on the order and extent of transfer. Step 4: To determine possible recombinant genotypes after Hfr conjugation, consider the gene order and the direction of transfer. Since the donor is A^+B^+C^+, and the recipient is ĀB̄C̄, the recipient may receive one or more wild-type alleles (A^+, B^+, C^+) replacing the mutant alleles. Possible recombinants include partial combinations such as A^+B̄C̄, A^+B^+C̄, or A^+B^+C^+, depending on how far the transfer proceeds before conjugation is interrupted. Step 5: Summarize that in (a), the recipient becomes F^+ but retains its original chromosomal genotype, while in (b), the recipient remains F^- but may acquire new chromosomal alleles from the Hfr donor, resulting in recombinant genotypes with mixed wild-type and mutant alleles.

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Key Concepts

Bacterial Conjugation and F Plasmid

Recombinant Genotypes from F⁺ × F⁻ Mating

Hfr Cells and Chromosomal Gene Transfer