Comparative positional candidate gene
A gene that is likely to be located in the same region as a DNA marker that has been shown to be linked to a single-locus trait or to a quantitative trait locus (QTL), where the gene's likely location in the genome of the species in question is based on its known location in the map of another species, i.e., is based on the comparative map between the two species.

Complement proteins
Proteins that bind to antibody-antigen complexes and help degrade the complexes by proteolysis.

Complementarity
The relationship between the two strands of a double helix of DNA. Thymine in one strand pairs with adenine in the other strand, and cytosine in one strand pairs with guanine in the other strand

Complementarity-determining regions
See CDR.

Complementary homopolymeric tailing
The process of adding complementary nucleotide extensions to different DNA molecules, e.g., dG (deoxyguanosine) to the 3' -hydroxyl ends of one DNA molecule and dC (deoxycytidine) to the 3 '-hydroxyl ends of another DNA molecule to facilitate, after mixing, the joining of the two DNA molecules by base pairing between the complementary extensions. Also called dG - dC tailing, dA - dT tailing.