cistron A section of the DNA molecule that specifies the formation of one polypeptide chain. A complementation test is performed to determine whether two mutant sites of a gene are in the same cistron or in different ones. In the cis configuration, both mutants are on one homologous chromosome and both wild-types are on the other (a¹a²/++), producing a wild-type phenotype. In the trans configuration each homologue has a mutant and a non-mutant (a¹+/a²+), producing a mutant phenotype.

cistron A section of the DNA molecule that specifies the formation of one polypeptide chain. A cis-trans test is performed to determine whether two mutant sites of a gene are in the same cistron or in different ones. In the cis configuration, both mutants are on one homologous chromosome and both wild types are on the other (a¹a²/++), producing a wild-type phenotype. In the trans configuration each homologue has a mutant and a non-mutant (a¹+/a²+), producing a mutant phenotype.

cistron A length of DNA that contains the information for coding a specific polypeptide chain or a functional RNA molecule (i.e. transfer RNA or ribosomal RNA). In the case of a protein, a cistron codes for a messenger RNA (mRNA) molecule. The cistron as a unit of function was defined by the cis-trans test: mutations occurring within a cistron affect the same function.