Velvet heterozygotes have a ruffled, silky coat, which is especially easy to classify on the ventral surface. Their vibrissae are straggly and can be classified by 10 days of age. Homozygotes die in utero and show ectodermal and endodermal defects as early as embryonic day 6.5.
The velvet coat mutation (Ve) was identified in the offspring of an X-irradiated male of unspecified genetic background in approximately 1964 at The Oak Ridge National Laboratory and was imported into The Jackson Laboratory in approximately 1964. Velvet was initially backcrossed to C57BL/10ScSn then to C57BL/6By for 24 generations, then, prior to 1978, Dr. Eva Eicher crossed this congenic to the congenic B6By.Cg-Ps. In 1983 the velvet and polysyndactyly mutations were separately backcrossed to C57BL/6JEi and this congenic subline was maintained by backcross of velvet heterozgyotes to C57BL/6JEi until 1984 when embryos were generated for cryopreservation from C57BL/6J females bred with heterozygous males at generation N22+6N3F1.