A new allelic series for the underwhite gene on mouse chromosome 15

A new allelic series at the underwhite gene is described. Three of the alle les in the series-uw, uw(d), and Uw(dbr)-arose as spontaneous mutations on different genetic backgrounds at The Jackson Laboratory. We report here the visible phenotypes and dominance hierarchy of these alleles, all of which are defined by a reduction of pigmentation in both eye and coat color. Elec tron microscopic analysis of retinal epithelium suggests that the primary d efect is in the melanosome. The degree of severity of melanosome anomalies in the retina correlates with the degree or hypopigmentation in the coat. T he perturbed gene and its gene product are unknown. We show that the uw loc us is genetically distinct from Myo10, a suggested candidate gene for this mutation.