Revertant

Revertant is a term used in genetics to describe an organism, cell, or lineage in which a previously mutated gene or trait has returned to a wild-type or functionally equivalent state. Reversion can refer to a change at the DNA level or to cellular and phenotypic restoration that eliminates the effects of the original mutation. The concept is central to studies of mutation, gene function, and genetic stability.

Mechanisms include true reversion (back mutation) where the original nucleotide change is reversed by a second mutation restoring the original sequence. Intragenic revertants occur within the same gene, while second-site revertants (or compensatory mutations) occur at a different locus and restore function by bypassing or compensating for the defect. Revertants can also arise via genetic recombination, gene conversion, or suppression by a tRNA or other factors that restore the phenotype without reversing the exact original sequence. The term does not always imply complete genetic restoration; phenotypic reversion may reflect partial restoration of function.

In multicellular organisms, revertant phenomena can appear as revertant mosaicism, where somatic mutations in some cells restore gene function, producing patches of normal tissue within a diseased background. This has been observed in several genetic disorders and has implications for disease progression and therapy, since reverting cells can influence phenotype and tissue function.

In laboratory genetics, revertants are used to study gene function and mutation effects and to validate gene complementation. The term is often contrasted with suppressor mutations, which alleviate the mutant phenotype without reversing the original DNA change.