The white-striped phenotype in white-throated sparrows is linked to a rearrangement of chromosome 2. Note that we follow conventional nomenclature for avian chromosomes, numbering them from largest to smallest (Ladjali-Mohammedi et al., 1999). Chromosome 2 in white-throated sparrows corresponds to chromosome 3 in chickens (Thomas et al., 2008). (A) Zebra finch BAC clones 55A1 and 5K13 both map to the long arm of ZAL2, but because of a series of inversions, they map to opposite arms of ZAL2m. (B) Fluorescent in situ hybridization shows the locations of the two clones (red and green) on ZAL2 and ZAL2m. Tan-striped (TS) birds have two copies of ZAL2 and white-striped (WS) birds have one copy of ZAL2 and one of ZAL2m. ZAL2m/ZAL2m homozygotes, or superwhite (SW) birds, are rare. The three birds shown in (C) are hatch-year females; at this age, the plumage is usually duller than in adults (compare to Fig. 1A). Nonetheless, this SW bird showed striking bright plumage even as a hatch year female. This bird also showed high levels of aggression (D), performing more displacements in one-on-one behavioral trials than TS or WS birds matched with same-morph opponents. Map of chromosome two (A) redrawn from Thomas et al. (2008). Photos in (B) and (C) reprinted from Horton et al. (2013) with permission. Data in (D) redrawn from Horton et al. (2013).