This allele has a null phenotype. Phenotypes of a alleles can be categorized in ~8 week old mice according to the amount of yellow, phaeomelanin, pigment vs black, eumelanic, pigment (J75206): MILD: Banded hairs are present on the dorsum, sides, and ventrum, with yellow hair around nipples, perineum, and behind ears. MODERATE: Banded hairs are present in all body regions, but with reduced yellow. Dorsum is moderately darker than sides adjacent to the ventrum. Yellow is prominent around nipples, perineum, and behind ears. UMBROUS-LIKE: Yellow is severely reduced along dorsal midline. Banded hair is present on the sides and ventrum but with reduced yellow. Yellow is also reduced around nipples, perineum, and behind ears. SEVERE: Yellow is severely reduced in dorsum, sides, and ventrum and moderately reduced around nipples, perineum, and behind ears. NULL: Hairs are completely black with no yellow banding. No yellow is present around nipples, perineum, and behind ears.