Molecular assay for morph determination. Molecular assay for morph determination in the white-throated sparrow, modified in the Tuttle laboratory for use on automated sequencers from primers described in . Panel A shows a tan morph with a single peak at 284 bp amplified from chromosome 2. Panel B shows a white morph with a band for chromosome 2 (at 284 bp) and two additional bands at 88 bp and 189 bp, which occur when PCR product amplified from chromosome 2m is digested with restriction endonuclease Dra I. If they occur in nature, we assume that birds homozygous for 2m ("super whites") would produce a pattern showing only the 88 bp and 189 bp bands. This technique has been verified in adults of known plumage. Values along the y-axis represent the intensity of fluorescence (a.u.), values along the x-axis mark the size of the DNA fragments (a function of time).