Corresponding or alike in certain critical attributes. (1) In biology or zoology, denoting organs or parts corresponding in evolutionary origin and similar to some extent in structure, but not necessarily similar in function. (2) In chemistry, denoting a single chemical series, differing by fixed increments. (3) In genetics, denoting chromosomes or chromosome parts identical with respect to their construction and genetic content. (4) In immunology, denoting serum or tissue derived from members of a single species, or an antibody with respect to the antigen that produced it. (5) Proteins having identical or similar functions (particularly with respect to proteins from different species).homologue [see homologue]