The origin of mutants under selection: Interactions of mutation, growth and selection

[This is a stub entry I'm making for John under his name. He should re-edit it with his own words. -- Eric]

Here’s the abstract to a new article.

The origin of mutants under selection: Interactions of mutation, growth and selection

Dan I Andersson, Diarmaid Hughes and John R Roth

In microbial genetics, positive selection detects rare cells with an altered growth phenotype (mutants or recombinants).  The frequency of mutants signals the rate of mutant formation – an increased frequency suggests a higher mutation rate.  Increases in mutant frequency are never attributed to growth under selection.  The converse is true in natural populations, where changes in phenotype frequency reflect selection, genetic drift or founder effects, but never changes in mutation rate.   The apparent conflict is resolved because restrictive rules allow laboratory selection to detect mutants without influencing their frequency.  With these rules, mutant frequency can reliably reflect mutation rates. When the rules are not followed, selection rather that mutation rate dictates mutant frequency – as in natural populations.  In several laboratory genetic systems, non-growing stressed populations show an increase in mutant frequency that has been attributed to stress-induced mutagenesis (adaptive mutation).  Since the mutant frequency is used to infer mutation rate (standard lab practice), the rules must be obeyed.  A breakdown of the rules in these systems may have allowed selection to cause frequency increases that were attributed to mutagenesis.  These systems have sparked interest in interactions between mutation and selection. This has led to a better understanding of how mutants arise, and how very frequent, small-effect mutations, such as duplications and amplifications, can contribute to mutant appearance by increasing gene dosage and mutational target size.

-- John Roth

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