Linkage tests, involving the dominant lethal mutation brachyury (short-tail), demonstrate that the gene responsible for this character is inherited independently of 14 other genes used as chromosome markers. The characters controlled by these 14 genes are: flexed-tail (anemia), albinism, chocolate, leaden, dilution, Robert''s pink-eye, naked, rodless, waltzing, Zavadskaia shaker, hairless, dominant spotting, dwarf, and hydrocephalus. The brachyury gene may be regarded as the marker of a 15th chromosome, unless linkage is subsequently found to exist among some of the 14 test genes now thought to be independent.