GENETIC-VARIATION IN QUANTITATIVE CHARACTERS OF MEIOTIC-GYNOGENETIC AND MITOTIC-GYNOGENETIC DIPLOID AYU, PLECOGLOSSUS-ALTIVELIS

Two types of gynogenetic diploids were artificially induced in the ayu, Plecoglossus altivelis, either by retaining the second polar body (the meiotic-G2N) or by suppressing the first cell cleavage (the mitotic-G2N) using a hydrostatic pressure shock of 650 kg/cm2 for 6 min applied to the fertilized eggs about 80 min after insemination. The success of inducing these two types of gynogenetic diploids was verified by an isozyme marker at the Gpi-1 locus. This showed a high percentage of heterozygosity in the meiotic-G2N and 0% heterozygosity in the mitotic-G2N. The mean, standard deviation, variance and coefficient of variation were calculated for various quantitative characters, such as body length and body weight, and some meristic characters, and these values were then compared among the control-2N and two types of G2N offspring. Except for a few characters which showed a small range of variation, there was a general tendency for the variance and coefficient of variation of the quantitative characters to be always large in the mitotic-G2N, small in the control-N and intermediate in the meiotic-G2N. These results are partly explained by formulae showing the correlation of increased phenotypic variance with increased genetic variance, increased coefficient of inbreeding, and deleterious effects of inbreeding. The expansion level of genetic variation in the two types of gynogenetic diploid may be a useful indicator for estimating heritability and the deleterious effects of inbreeding on various quantitative characters. © 1990.