complementation

Complementation refers to the act or process of completing something by supplying what is lacking. In genetics, complementation describes a relationship between two organisms carrying recessive mutations in different genes: when crossed, the offspring display a wild-type phenotype because each mutant provides the functional copy of the gene the other lacks. This genetic complementation test helps determine whether two mutations affect the same gene (no complementation) or different genes (complementation). Complementation can also refer to rescuing a mutant phenotype by introducing a wild-type copy of the gene, a strategy used in functional analysis and cloning.

In mathematics and logic, the complement of a set A with respect to a universal set U is the set of elements of U not in A. The complement operation corresponds to logical negation and underpins De Morgan's laws, with applications ranging from set theory to digital circuits.

In lattice theory and Boolean algebra, a complemented structure is one in which elements have defined relative complements, generalizing the idea of a set complement.

In biology, protein complementation assays use fragments of a reporter protein that reassemble when two proteins of interest interact, generating a detectable signal and enabling studies of protein–protein interactions. These approaches often aid in mapping interaction networks and validating functional partnerships.