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Abstract

Recent surveys of the human genome have highlighted the significance of balancing selection in relation to understanding the evolutionary origins of disease-associated variation. Cis-regulatory variation at the blood group–related glycosyltransferase B4galnt2 is associated with a phenotype in mice that closely resembles a common human bleeding disorder, von Willebrand disease. In this study, we have performed a survey of the 5′ flanking region of the B4galnt2 gene in several Mus musculus subspecies and Mus spretus. Our results reveal a clear pattern of trans-species polymorphism and indicate that allele classes conferring alternative tissue-specific expression patterns have been maintained for >2.8 My in the genus Mus. Furthermore, analysis of B4galnt2 expression patterns revealed the presence of an additional functional class of alleles, supporting a role for gastrointestinal phenotypes in the long-term maintenance of expression variation at this gene.