20. The concept of recon was proposed by Seymour Benzerby studying recombination between
(1) lysis mutants of bacteriophage T4
(2) white eye mutants of Drosophila melanogaster.
(3) biochemical mutants of Neurosporacrassa.
(4) auxotrophic mutants of Escherichia coli.
Explanation
Benzer’s classic work used the rII region of bacteriophage T4, where many different lysis mutants all failed to grow on a particular E. coli strain. By co‑infecting bacteria with pairs of different rII mutants and scoring rare wild‑type recombinants (plaques), he could measure recombination between mutations lying within a single gene. From this he concluded that:
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The gene is a linear array of sites.
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The smallest unit that can be separated by recombination is on the order of a single nucleotide.
He named this smallest recombination unit the “recon”.
Option-by-option:
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Lysis mutants of bacteriophage T4 – correct
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These rII lysis mutants were the exact system Benzer used to define recon (and also cistron and muton).
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White eye mutants of Drosophila melanogaster
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Drosophila eye-color mutants were pivotal for early linkage and complementation studies (e.g., Morgan, Sturtevant, Lewis), but the fine-structure mapping that led to the recon concept was done in T4 phage, not in flies.
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Biochemical mutants of Neurospora crassa
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Neurospora biochemical mutants (Beadle and Tatum) established the “one gene–one enzyme” concept, focusing on gene–enzyme relationships, not on defining the smallest recombination unit within a gene.
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Auxotrophic mutants of Escherichia coli
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E. coli auxotrophs are widely used in microbial genetics and recombination studies, but Benzer’s recon work specifically involved T4 rII mutants, not bacterial auxotrophs themselves.
Thus, the recon concept was proposed from recombination analysis of lysis mutants of bacteriophage T4 (option 1).
