Molecular Marker Development And Linkage Mapping In The Pacific Oyster Crassostrea Gigas Thunberg

Amplified fragment length polymorphisms (AFLPs), Random Amplified Polymorphic DNA (RAPD) and microsatellite markers were used for genome mapping in the Pacific oyster, Crassostrea gigas Thunberg. Seventeen selected AFLP primer combinations produced 1106 peaks, of which 384 (34.7%) were polymorphic in a backcross family. Among the polymorphic markers, 349 were segregating through either the female or the male parent. Chi-square analysis indicated that 255 (73.1 %) markers segregated in Mendelian ratio, and 94 (26.9%) showed significant (p<0.05) segregation distortion. For RAPD, 33 selected primers produced 338 bands, among which, 102 (30.2%) were polymorphic between the parents. Ninety-four segregating markers were identified, among which 74 (78.7%) were in agreement with 1:1 Mendelian ratio, and 20 (21.3%) were distorted markers. Among the 55 microsatellite markers screened, 13 and 11 microsatellite loci were heterozygous in the female and the male parent, respectively. Among all the microsatellite loci, 46.7% of the loci and 11.7% of the alleles were null alleles. Separate genetic linkage maps were constructed for the female and male parents. The female framework map consisted of 130 markers (119 AFLP and 11 microsatellite markers) in 11 linkage groups, spanning 1057.9 cM with an average interval of 8.9 cM per marker. The male map contained 105 markers (96 AFLP, 8 microsatellite markers and 1 sex-determination marker) in 10 linkage groups, covering 820.9 cM with 8.6 cM per marker. The estimated genome length of the Pacific oyster was 1263.0 cM for the female and 989.7 cM for the male, and the observed coverage was 83.8% for the female and 82.9% for male map.Through comparisons of the female and male maps, 5 pairs of homologous linkagegroups and 2 syntenic region were identified. Most distorted markers were deficient for homozygotes and closely linked to each other on the genetic map. At least four recessive lethal genes were inferred in the mapping family. The fact that the sex-determination marker was only mapped in the male map indicated that the male Pacific oyster could be heterogametic sex.