A number of single gene mutations in laboratory mice produce hair follicle defects resulting in deformed hair shafts. The radiation‐induced (SB/LeJ‐Foxq1sa) satin mutant mice have a satin‐like sheen to their hair and dilute colouration. This sheen is due to failure of the hair shafts to develop normal medullas, while the pigment dilution is due to the unrelated beige (lysosomal trafficking regulator, Lystbg) mutation. A new allelic mutation, Foxq1sa‐J, arose spontaneously on the albino (tyrosinase, Tyrc) MRL/MpJ‐Faslpr background. The Foxq1sa‐J allele has a C to T transition at position 490. By contrast, the Foxq1sa mutant allele was confirmed to be a 67 base pair deletion followed by two base changes (GA to AT). Morphologic changes were similar to those seen in Hoxc13 transgenic and targeted mutant mice. This new allelic mutation provides yet another tool to investigate formation of the interior structures of hair shafts.