Abstract: The gene responsible for the autosomal recessive mouse obesity mutation tub was identified by positional cloning. The homologous human gene is also provided. The genes are used to produce tubby protein; in screening for compositions that modulate the expression or function of the tubby protein; and in studying associated physiological pathways. The DNA is further used as a diagnostic for genetic predisposition to obesity, retinal degeneration or cochlear degeneration. The mutation responsible for the tub phenotype is a G to T transversion that abolishes a donor splice site in the 3' coding region and results in a larger transcript containing the unspliced intron. A second, prematurely truncated transcript arises from the introduction of a premature polyadenylation site in the unspliced intron.