A complementation test is used in genetics to decide if two recessivemutantphenotypes are determined by mutations in the same gene or two different genes. True breeding mutants are crossed bringing together the mutant genotypes in an F1 individual. If that individual is mutant, then the complementation has failed, and thus the two alleles are the same gene. If no mutant phenotype is observed in the F1 individual, then the mutant alleles are complemented and must be different genes.
That is:
If the combination of two haploid genomes containing different recessive mutations yields a mutant phenotype, then the mutations must be in the same gene (alleles).
If the combination of two haploid genomes containing different recessive mutations yields the wild type phenotype, then the mutations must be in different genes.
There is an exception to this rule. Two non-allelic mutants may fail to complement (called "non-allelic non-complementation" or "unlinked non-complementation"). This situation is rare and is dependent on the particular nature of the mutants being tested. For example, two mutations may be synthetically dominant negative.
Complement proteins are produced constitutively by macrophages and hepatocytes, and are present in the circulation as inactive molecules.
Complement components are numbered in the order in which they were discovered, which fortunately is almost the same as the order in which they function in the activation cascade.
Complement activity is regulated by serum levels of complement components, natural decay of the activated fragments, serum protease inhibitors, and specific complement inhibitors.
The word complement (with an e in the second syllable, not to be confused with a different word, compliment with an i) has a number of uses.
complement (biology) is a group of proteins of the complement system, found in blood serum which act in concert with antibodies to achieve the destruction of non-self particles such as foreign blood cells or bacteria.
In traditional music theory a complement (music) is the interval added to another, that is placed on top of another, so that their complete span is an octave, while in musical set theory the complement of a pitch class set are those pitches not included (the pitches needed to form an aggregate).
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