This ENU-induced mutation was isolated in a screen at the University of Pittsburgh. It is a subline of b2b2736Clo. The molecular lesion is a G to A substitution at nucleotide +1 after coding nucleotide 103 (c.103+1G>A, NM_007685) in intron 2, changing splice donor site A-GT to A-AT (which is assumed to be inactive or much less efficient).