- Biology. a type specimen of the sex opposite to that of the holotype.
- Immunology. an antibody of a given class having certain molecular sites shared by only some members of a species and therefore acting as an antigen to other members of the same species.
- biology an additional type specimen selected because of differences from the original type specimen, such as opposite sex or morphological details
- immunol any of the variant forms of a particular immunoglobulin found among members of the same species
- Any of the genetically determined variants in the constant region of a given subclass of immunoglobulin that is detectable as an antigen by members of the same species having a different constant region.