The Relationship Between Morphological Characters And Body Weight And SNP Marker Screening Associated With Growth Traits Of Grass Carp(Ctenopharyngodon Idella)

As fast growth, good taste and low breeding cost, grass carp is one of the four cultured freshwater fish species in China. However, wild grass carps were used to breed until now and no gene improved due to long mature period and large bodies of parents. To improve breeding selection more efficiency and quickly, we identified the effects of morphological attributes on body weight of grass carp in this study. Meanwhile, SNPs markers were selected from EST-SNPs database of grass carp. SNPs which associated with growth traits were also analyzed. The detailed contents as follows:1. To study the effects of morphological attributes on body weight of grass carp, seven metric traits were measured from287individuals of2-year-old, including total length, standard length, head length, body width, body height, interorbital width, length before anus.The relationships between major morphological attributes morphological body weight were examined by correlation analysis, path analysis and multiple regression analysis, respectively. Results showed that the correlation coefficients of each morphological trait to body weight were all of significance. Head length, body height were eliminated from the variable data due to no significances in multiple regression analysis. Total length was also kicked out because it was co-linear with standard length. The regression equation was:Y=-3048.127+220.925X4+262.367X6+33.776X7+10.648X2, in which body weight was dependent variable, while body width, interorbital width, length before anus, standard length were independent variables. Main variables were selected from high correlation index, among which body width was the most effective factor on body weight. During the selected process, essential theoretical basis and ideal measure for selective breeding of grass carp were suggested when four main morphological traits considered as a whole.2. Forty-four SNPs were found from EST-SNPs database of grass carp which located in aldolase A, fructose-bisphosphate, muscle creatine kinnase, chymotrypsinogen, MHY mRNA for myosin heavy chain embryonic type I, MAPK, ribosomal output protein S7, asparagine-tRNA synthetase,β-actin, macroglobulin, skeletal muscle myosin heavy chain, fast skeletal myosin heavy chain, β-2-globin beta globulin, PGC. beta-2-macroglobulin. According to function, they can be divided into four categories:the key enzyme of glucose metabolism, immune factors, muscle growth factor, protein synthase.25SNPs located in exons, introns and untranslated regions, including transitions, transversions, insertional mutagenesis. Exon mutations included missense mutations and synonymous mutations, synonymous mutation changed the coding of amino acids but no differences in gene function. In this study,17synonymous mutationsand7missense were found, showing that the numbers of synonymous mutations were more than missense mutation, the amino acid sequence was the consequence from a long-term evolution of biological. The proportion of18conversion and8transversion is2:1, and this ratio is the same with others. Aldolase A3’UTR17bp insert and muscle growth factor muscle creatine kinase were selectively analyzed. The results showed that17bp insert fragment was exist at58bp after the stop codon. A mutation was found in muscle creatine kinase gene178bp at exon7. This mutation original encoding changed serine into threonine. Analysing the secondary structure of encoding protein, numbers and types of corner of Alpha and Beta were also changed. Therefore, results from this study provided the important foundation for subsequent growth traits associated analysis.3. Genotypes of eight SNPs were selected from the13functional genes in294individuals of grass carp using a new technology-Snapshot. They were found in aldolase A, Beta-microglobulin, chymotrypsin, creatine kinase, skeletal muscle myosin heavy chain. Only T-A mutation located in skeletal muscle myosin heavy chain was detected one genotype, others were detected AA、BB、AB three genotypes in groups. A general linear model was used for association analysis between genotype in seven SNPs and growth traits, showing that17bp insert in aldolase A3’UTR and the missense in muscle creatine kinase were significantly correlated with the growth of fishes. Results showed that body width and snout length were significantly associated with aldolase A3’-UTR mutation. Body weight, body width, length before anus were significantly associated with three genotypes in muscle creatine kinase. TT individuals had an advantage which could be a molecular marker for growth traits selective breeding in grass carp.