Evidence for the formation of the male gynogenetic fish.

The females and unexpected males of gynogenetic red crucian carps (GRCC) with the 1:1 sex ratio were found in the progeny of the distant crossing of red crucian carp (RCC; female symbol, 2n = 100) x blunt snout bream (BSB; male symbol, 2n = 48). The females and males of GRCC were fertile, and they mated each other to generate the red crucian carps (GRCC(1)) and another variational gray crucian carps (GGCC). The GRCC and their offspring were proved to be diploids (2n = 100) with one to three microchromosomes by examining the chromosomal metaphases. The evidences for the male's genetic effect in GRCC were provided by means of fluorescence in situ hybridization, Sox-HMG DNA markers, and microsatellite DNA markers. The genotypic variances of GRCC resulted in their phenotypic variances which were quite different from their maternal parent. It was concluded that the formation of the male gynogenetic fish in GRCC resulted from the genetic leakage of the paternal fish in the form of the microchromosomes including the paternal male-determining gene. After being activated by the sperm of BSB, which was inactivated and finally degraded but left the microchromosomes, the egg of RCC, in which the 50 chromosomes were spontaneously doubled to 100 chromosomes, developed into the diploid male gynogenetic fish. The formation of the bisexual GRCC and their progeny indicated that the distant hybridization could generate the bisexual diploid gynogenetic fish with genetic variation derived from the paternal fish, which is of great significance in both fish genetic breeding and evolutionary biology.