Female guppies (Poecilia reticulata) generally lack the conspicuous ornamental pigmentation characteristic of males, although the underlying genetic determinants of coloration are present in both sexes. This mini-review examines the genetic, chromosomal, hormonal, developmental, and evolutionary mechanisms underlying sex-limited pigmentation in guppies, with particular emphasis on the relationship between sex linkage, recombination, and phenotypic expression. The guppy possesses an XY sex-determination system on chromosome pair 12, and current genomic, cytogenetic, and linkage evidence indicates that its sex chromosomes remain largely homomorphic and retain substantial regions capable of X–Y recombination. Rather than forming a simple nonrecombining block, chromosome 12 exhibits a recombination gradient, with strongly reduced exchange around the sex-determining region and progressively higher recombination toward the distal pseudoautosomal region. Classical genetic studies have demonstrated extensive Y-linked inheritance of male coloration, together with X- and Y-linked loci whose expression is restricted to males and a smaller contribution from autosomal loci. The absence of ornamental coloration in females therefore reflects predominantly sex-limited and hormonally regulated gene expression rather than the absence of pigmentation genes. Experimental androgen treatment can induce male-like coloration in females, further supporting a regulatory basis for sexual dimorphism. In domesticated ornamental strains, this regulatory restriction can be altered, allowing certain dominant sex-linked color patterns to be expressed in females. The developmental formation of pigmentation involves temporally distinct pigment-cell populations and signaling pathways associated with melanophore, xanthophore, and iridophore differentiation. Finally, female mate choice and predation jointly shape the evolution and maintenance of male coloration, while variation in visual sensitivity may contribute to coevolution between female perception and male ornamental traits. Overall, guppy pigmentation provides a particularly informative model for understanding how chromosome structure, recombination, hormonal regulation, and sexual selection interact to produce sexually dimorphic phenotypes.
