Since the early 1950’s, Singapore is internationally known as the guppy-breeding centre. At least 40 different colour varieties of guppies are cultured in Singapore, with each farm specialising in 10 to 15 varieties. These fancy varieties have been developed by skilful farmers through intensive and continual selective breeding. Genes controlling background body pigmentation such as albino (a), blond (b), gold (g) and blue (r) are autosomally inherited and recessive to their wild-type alleles which produce drab olive-brown background coloration. Colour patterns which are superimposed onto wild-type background coloration are due to genes located on the sex chromosomes. These
sex-linked colour genes are dominant and sex-limited to males as their expression requires male hormones. Y-linked colour pattern genes carried by males are inherited only along the paternal line while X-linked genes are present in both sexes. Among the guppy varieties produced locally, only two Y-linked genes, Ssb and Sst, that control snakeskin tail and body patterns, respectively, have been found in varieties with snakeskin-like reticulations. Single colour genes that are both X- and Y-linked produce red (Rdt), blue (Blt), green (Grt), black (Bt) and variegated (Var) patterns
on the caudal fin. The black caudal-peduncle of the Tuxedo variety is the result of Bcp, a gene that is both X- and Ylinked. Different combinations of colour pattern genes and background pigmentation genes as well as interactions among them give rise to various colour phenotypes. For
instance, the inclusion of Bcp in Snakeskin varieties causes black reticulations on the tail fin to be replaced by large, coarse black spots. Neon coloration is produced by interactions between the Ln (light turquoise) gene with Blt, Rdt and Bcp.