Agouti expression during the middle portion of the mouse hair growth cycle induces melanocytes to synthesize yellow instead of black pigment, generating black hairs with a yellow band. Dominant agouti alleles increase the amount of yellow pigment in the coat and are associated with pleiotropic effects including obesity, diabetes and increased tumor susceptibility. Four dominant agouti alleles (Aiapy, Aiy, Asy and Avy) were recently shown to result from insertions that cause ubiquitous expression of chimeric transcripts encoding a wild‐type agouti protein(1,2). (...) Three insertions were identified as intracisternal A‐particles, which helps explain the variable coat colors and parental imprinting effects associated with some dominat agouti alleles. (shrink)