Genetic basis of the variegated tail pattern in the guppy, Poecilia reticulata

Variegated patterns on the caudal fin are a common and popular trait in gup py strains commercially cultured in Singapore. Gene control of this highly variable mosaic pattern of black spots and patches of different shapes and sizes on a brightly colored tail fin was elucidated by reciprocal crosses b etween the Green Variegated (GV) strain and wild-type (WT) stock. F-1 proge nies were produced by single-pair crossing between GV and WT, while the F-2 generation was obtained from full-sib mating between F-1 males and F-1 fem ales. Data for the F-1 and F-2 generations were segregated according to phe notypes and sex, and tested by chi-square analyses. Inheritance of variegat ed tail patterns appears to be determined by a single locus on the X- and Y -chromosomes. Genotypes of males and females of the GV strain are proposed to be XVarYVar and XVarXVar, respectively. The allele for variegated tail p atterning, Var, is dominant over that of the wild-type, Var(+), which does not exhibit these patterns. Recombination frequency between the Var locus a nd sex-determining region (SdR) in male guppies was estimated to be about 1 .9% (map distance approximate to 1.9 map units). The segregation and mode o f inheritance of the Var gene are illustrated by genetic models.