While variable regions of immunoglobulins are extensively diversified by V(D)J recombination and somatic hypermutation in vertebrates, the constant regions of immunoglobulin heavy chains also utilize certain mechanisms to produce diversity, including class switch recombination (CSR), subclass differentiation, and alternative expression of the same gene. Many species of birds, reptiles, and amphibians express a truncated isoform of immunoglobulin Y (IgY), termed IgY(ΔFc), which lacks the υCH3 and υCH4 domains. In Anseriformes, IgY(ΔFc) arises from alternative transcriptional termination sites within the same υ gene, whereas in some turtles, intact IgY and IgY(ΔFc) are encoded by distinct genes. Different from the previously reported IgY(ΔFc) variants, this study identified a truncated IgY in the snake