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Shell coloration in many molluscs is highly variable. A shell color segregation study with progenies from a full factorial cross generated among Pacific oysters exhibiting distinct shell colors (golden, white and black) was conducted to investigate the inheritance of the golden shell color and its correlation with dark pigmentation. Random samples from twenty-three full-sib families were obtained and the shell coloration of offspring within each family was recorded. Results revealed that golden coloration was inherited in a different pattern from dark pigmentation, indicating its different genetic basis. Dark pigmentation was identified as a foreground color while golden or white color were background ones. The locus controlling background colors has two alleles with the allele for golden background being dominant to the allele for white background. In addition, the overlying foreground pigmentation of shells with a golden background was significantly lighter than that of shells with a white background, which suggested an epistatic effect of background color on shell foreground pigmentation. All these findings will facilitate the selection of elite oyster lines with desired shell coloration for aquaculture. [ABSTRACT FROM AUTHOR]

The Pacific oyster (Crassostrea gigas) is one of the most important species which has the largest production among all cultured shellfish. Recently, several shell color strains of C. gigas have been developed to improve the commercial values, however the inheritance of shell pigmentation is still unclear. A total of 29 families cross-mated between different pigmented oysters were produced to investigate the inheritance of the shell pigmentation and purple pigmentation. Random samples from each family were obtained and their shell pigmentation were recorded. Results revealed that shell pigmentation was controlled by two genetic locus, among which one is responsible for secretion of pigmentation and the other is responsible for distribution mode of pigmentation. The locus controlling the secretion of pigmentation has two alleles with the allele for the presence of pigmentation being dominant to the allele for the absence of pigmentation. Similarly, another locus controlling the distribution mode of pigmentation has two alleles with the allele for striped distribution being dominant to the allele for solid distribution. In addition, one independent locus with two alleles was suggested to control the purple-striped pigmentation, which one allele for shell devoid of purple pigmentation is dominant to another allele for shell with purple pigmentation. The findings will provide valuable information for the efficient selective breeding of shell color strains in the Pacific oyster. • A two-locus model for inheritance of shell pigmentation were demonstrated. • The allele for secretion of pigmentation is dominant to the other allele for absence of pigmentation. • The allele for striped distribution of pigmentation is dominant to the allele for solid distribution of pigmentation. • An indenpendent loci was found to control the inheritance of purple striped pigmentation. [ABSTRACT FROM AUTHOR]

Shell color polymorphism is common in nature for the marine mollusks. The Pacific oyster Crassostrea gigas , is widely cultured and one of the most economically important bivalve species with various shell color variants. Here, a total of 1061 single nucleotide polymorphism markers, developed from expressed sequence tags (EST-SNPs), were used to construct two genetic linkage maps based on reciprocal-cross between black shell and white shell oysters (MF-A and MF-B) respectively. The two separate linkage maps were combined into an integrated map spanning 947.31 cM in total length. The integrated map was composed of 351 EST-SNP markers distributing on 10 linkage groups, with an average interval of 2.78 cM between adjacent markers. For the MF-A, 11 quantitative trait loci (QTLs) for shell color traits and five QTLs for growth traits were detected, explaining 8.1%–13.8% (mean = 11.76%) and 10.4%–11.0% (mean = 10.66%) phenotypic variance respectively. For the MF-B, nine QTLs for shell color traits and eight QTLs for growth traits were detected, explaining 8.8%–21.7% (mean = 12.84%) and 8.4%–9.4% (mean = 8.88%) phenotypic variance respectively. QTLs clustering was found on the linkage group 2 of the MF-A and the linkage group 8 of the MF-B, and the QTLs showed that pleiotropism could affect at most three traits. Three shared-QTLs associated with shell color traits were identified on the integrated map, and one of them (qA- a * 4) was significantly homologous to C. gigas calmodulin-like protein. The QTLs identified in the present study could be useful in finding candidate genes for the shell color and growth-related traits in future, and potentially applied to marker-assisted selection breeding programs for C. gigas . [ABSTRACT FROM AUTHOR]

Molluscan shellfish have a diverse form of shell coloration and sex determination, understanding the genetic mechanism under these two traits is crucial to their germplasm exploitation and conservation. In our breeding program, a novel orange-shell variant of C. gigas was obtained, and an F2 family was constructed by crossing an orange-shell male with a black-shell female. This F2 family provided an ideal material for QTL mapping of orange shell color and sex traits of C. gigas simultaneously. Here, a high-density genetic linkage map containing 1799 SNP markers was constructed using this F2 family by genotyping-by-sequencing. These markers were distributed on 10 linkage groups and the total map size was 828.31 cM, with an average marker interval of 0.58 cM. Based on this map, six chromosome-level significant QTLs associated with orange shell color were detected, with the phenotypic variance explained ranging from 9.10% to 12.30%. Within the QTL regions, four candidate genes, 3-ketoacyl-CoA thiolase A, fibroblast growth factor receptor 4, poly [ADP-ribose] polymerase tankyrase-1 and tripartite motif-containing protein 45-like, related to the organic matrix of mollusk shells or collagen were identified. Additionally, only one genome-wide significant sex-related QTL was detected, which explained 19.30% of phenotypic variance. Two sex-related genes, proteasome subunit beta type-3 and G-protein coupled estrogen receptor 1 were identified within the QTL region. The QTLs and candidate genes identified in this study provide valuable resources for further investigations on the molecular mechanisms of shell color and sex in C. gigas. • A high-density genetic linkage map containing 1799 SNP markers was constructed for C. gigas using an F2 family. • Six chromosome-level significant QTLs associate with orange shell color were detected in C. gigas. • Only one genome-wide significant sex-related QTL was detected in C. gigas. • Different description methods of phenotype have a great impact on the result of QTL mapping. [ABSTRACT FROM AUTHOR]