- Ig Y is the main serum immunoglobulin of amphibians, birds and reptiles.
- Ig Y considered to be the functional equivalent of mammalian IgG.
- Ig Y also shows similarity to IgE by mediating anaphylactic reactions in some species.
- Mammalian, IgG and IgE are believed to have formed as the result of the duplication and divergence of Ig Y.
- The upsilon chain is composed of one V-DOMAIN and four C-DOMAINs.
 Warr, G. W. et al. Immunology Today 16, 392-398 (1995).