23. Conjugation involves transfer of DNA from one cell to another. In E. coli, the cells that cannot transfer their DNA into the recipient cell are
(1) Hfr           (2) F’
(3) F⁺               (4) F^–

Introduction
E coli conjugation cells cannot transfer DNA refers to bacterial genetic exchange where donor cells with F plasmid transfer DNA via a pilus to recipients. In E. coli, this process distinguishes donor types like Hfr, F+, and F’ from recipients, crucial for CSIR NET Life Sciences exam prep on horizontal gene transfer. Understanding which E coli conjugation cells cannot transfer DNA helps clarify donor-recipient dynamics in molecular genetics.​

Question and Correct Answer

Conjugation involves transfer of DNA from one cell to another. In E. coli, the cells that cannot transfer their DNA into the recipient cell are (4) F-. F- cells lack the F plasmid, acting only as recipients without sex pili for initiating transfer. This unidirectional process ensures DNA moves solely from donors to F- recipients during conjugation.​

Option-by-Option Analysis

• (1) Hfr: High frequency recombination (Hfr) cells integrate the F plasmid into their chromosome, enabling transfer of chromosomal DNA alongside F factor to recipients via conjugation pilus. They actively donate large DNA segments, unlike non-donors.​

• (2) F’: F prime (F’) cells carry an F plasmid with chromosomal genes excised from Hfr, allowing transfer of both plasmid and extra genes to F- recipients during conjugation. These donors spread hybrid plasmids efficiently.​

• (3) F+: F+ cells possess autonomous F plasmids, producing sex pili to transfer complete F plasmid copies to F- recipients, converting them to F+. F+ donors initiate conjugation rapidly across populations.​

• (4) F- (Correct): F- cells lack F plasmid and sex pili, preventing DNA transfer; they receive but cannot donate, remaining recipients post-conjugation. This defines their role in E coli conjugation experiments.