Microsatellite-centromere mapping in sea cucumber (Apostichopus japonicus) using gynogenetic diploid families

Two families of gynogenetic sea cucumber (Apostichopus japonicu) were produced by fertilizing eggs with UV-irradiated sperm followed by inhibition of the second meiotic division. Inheritance of 43 microsatellite markers were examined in the two meiogynogenetic diploid families for centromere mapping using half-tetrad analysis. The ratio of gynogenesis was proven to be 93.3% and 100% in the two families, respectively. Inheritance analyses in the control crosses showed that 2.3% microsatellite loci deviated from Mendelian ratios. The second division segregation frequency (y) of the microsatellites ranged from 0.00 to 0.80, suggesting the existence of positive interference after a single chiasma formation. The mean recombination frequency was 0.21, corresponding to a fixation index of 0.79 in one generation. This is 3.2 times the expected increase in homozygosity after one generation of sib mating (0.25), suggesting meiotic gynogenesis may be an effective means of rapid inbreeding in the sea cucumber. Microsatellite-centromere distances ranged from 0.0 cM to 40.0 cM under the assumption of complete interference. The information about the positions of centromeres in relation to the microsatellite loci will be useful for the future gene mapping in this commercially important species.