22. In E. coli gal⁺ and bio⁺ genes are located very near to each other on genome. A bacterium with F’ gal⁺ on conjugation with F^– can lead to diploid condition for
(1) gal only
(2) bio only
(3) gal and bio both
(4) E. coli will always remain haploid

In E. coli, the gal+ (galactose utilization) and bio+ (biotin synthesis) genes are closely linked near 17 minutes on the chromosome, flanking the lambda phage attachment site. During conjugation, an F’ gal+ plasmid—a fertility factor carrying this chromosomal segment—transfers from the donor (F’ gal+) to the F- recipient, creating a merodiploid (partial diploid) state with both chromosomal and plasmid copies of these genes. The correct answer is option (3) gal and bio both, as the F’ carries the entire nearby region, duplicating both loci in the recipient.

Option Analysis

• (1) gal only: Incorrect. F’ plasmids excise chromosomal segments including nearby genes; since gal+ and bio+ are adjacent (gal at ~17 min, bio nearby), the F’ gal+ includes bio+, not isolating gal.

• (2) bio only: Incorrect. The notation F’ gal+ specifies gal as the marker, but proximity ensures bio+ co-transfer; isolated bio diploidy would require F’ bio, not F’ gal+.

• (3) gal and bio both: Correct. Close linkage (within lambda integration region) means imprecise F’ excision captures both, yielding F’ gal+ bio+/chromosomal diploidy via stable plasmid replication.

• (4) E. coli will always remain haploid: Incorrect. F’ transfer creates autonomous extrachromosomal replication, producing meridiploids for transferred genes, unlike Hfr (linear transfer, rarely complete).

Mechanism Overview

F’ plasmids form when integrated F (Hfr) excises aberrantly, incorporating adjacent chromosomal DNA like gal-bio. Conjugation transfers the single-stranded F’ via sex pilus to F-, where it circularizes and replicates independently, yielding stable diploids for analysis (e.g., complementation tests). This differs from F+ (F-only transfer) or Hfr (chromosomal strand transfer, no plasmid stability).

CSIR NET Relevance

This tests bacterial genetics linkage, F’ merodiploids, and conjugation outcomes—core for CSIR NET Life Sciences (Molecular Genetics unit). Partial diploids enable dominance/recessive studies without full genome duplication.