Linkage analysis and mapping of three sex-linked color pattern genes in the guppy, Poecilia reticulata

Abstract

Three phenotypic color pattern genes of the guppy (Poecilia reticulata), i.e., black caudalpeduncle (Bcp), red tail (Rdt) and variegated tail patterning (Var), were genetically analyzed and mapped. Crosses between the Tuxedo (TUX) and Green Variegated (GV) guppy strains commercially cultured in Singapore were used to determine the gene control of these color patterns. F1 progenies were produced by single-pair reciprocal crossing between TUX and GV, while the F2 generation was obtained from full-sib mating between F1 males and females. F1 and F2 data were segregated according to color phenotypes and sex, and tested by chi-square analyses. The Bcp, Rdt and Var color pattern genes, located at different loci on the X-and Y-chromosomes, showed single gene inheritance and dominant expression in both sexes. Their corresponding recessive alleles, Bcp+, Rdt+ and Var+ do not produce any color patterns. Genotypes of Tuxedo males are proposed to be XBcp,Rdt,Var +YBcp,Rdt,Var + (type I), XBcp +,Rdt,Var +YBcp,Rdt,Var + (type II) and XBcp,Rdt,Var +YBcp +,Rdt,Var + (type III) while females are XBcp,Rdt,Var +XBcp,Rdt,Var +. Green Variegated males and females have the XBcp +,Rdt +,VarYBcp +,Rdt +,Var and XBcp +,Rdt +,VarXBcp +,Rdt +,Var genotypes, respectively. Close linkages of 3.1, 2.3 and 2.2 map units were estimated for the sex-determining region (SdR)-Rdt, Rdt-Bcp, and SdR-Var gene pairs, respectively, while Bcp was approximately 5.1 map units from the SdR. The phenotypic map order of the guppy Y-chromosome is inferred to be Var-SdR-Rdt-Bcp.