Detection of Hereditary Dwarfism in the Guppy

To elucidate genetic control for the growth of the guppy, size differences between Fancy (F) and Standard (S3) strains and between dwarf and normal in the F strain were examined. The two guppy strains, F and S3, displayed significant differences in growth. The F strain is bigger than the S3 strain in body length at Day 60. Using strain comparison, the heritability (Va/Vp) was estimated at 59. 2% in females and 38. 6% in males. Thus, the strain difference indicates the proportion of genetic determination of the character. Dwarf guppies were found in some of the inbred litter of brother-sister mating of the F strain. An overlap of distributions for body length at Day 60 was observed between F and S3 strains but not between dwarf and normal. From the comparison between dwarf and normal, the heritability was estimated at 88. 0 % to normal females and 84 5 % to normal males. These high values suggest that the dwarf is induced by a single gene with major effects on what is ordinarily growth. A single gene inheritance was supported by the segregation of the dwarf in some of the litter of inbreeding pedigree.