MyoG和MEF2a基因多态性聚合效应对鸭屠宰性状的影响

【目的】探讨MyoG和MEF2a基因聚合效应对鸭屠宰性状的影响，为进一步确定与鸭屠宰性状相关的分子遗传标记提供研究基础，为鸭屠宰性状的多基因聚合育种提供依据。【方法】试验以240只三穗鸭为研究素材，扩增MyoG和MEF2a基因并进行PCR产物直接测序以检测两基因所有外显子的单核苷酸突变（SNPs）位点。运用SPSS 18.0软件中的GLM统计模型对MyoG和MEF2a基因的SNPs所对应的不同基因型与三穗鸭屠宰性状进行关联分析，根据单基因关联分析结果，将对屠宰性状存在显著影响的MyoG和MEF2a基因的多态位点利用软件PHASE 2.0构建聚合基因型，再进行聚合基因型与屠宰性状的关联分析。【结果】在试验群体中一共发现8个SNPs，其中在MyoG基因中有6个SNPs被找到，MEF2a基因中找到2个SNPs位点，在所有突变位点中，其中MyoG基因的g.2977G＞C位点发生的G/C突变使密码子由GAG变为GAC，所编码的氨基酸由谷氨酸变成天冬氨酸；而MEF2a基因中的两个多态位点，g.47915G＞A位点发生的G/A突变使密码子由GAA变为AAA，编码的氨基酸由谷氨酸变成赖氨酸，g.47918G＞A位点的G/A突变引起的密码子由GAT变成AAT，所编码的氨基酸由天冬氨酸变成天冬酰胺。剩下的5个突变位点均属于同义突变，并未引起编码氨基酸的改变。此外，进行?2适合性检验，除了MyoG基因的g.1131C＞T位点和MEF2a基因的g.47915G＞A、g.47918G＞A位点未处于Hardy-Weinberg平衡状态（P＜0.05）外，其他的突变位点均处于平衡状态。单基因关联分析结果表明，MyoG基因g.1131C＞T和g.2204G＞A突变分别对胸肌率、体重和全净膛重有着显著影响，其所对应的纯合子基因型CC、GG型为优势基因型。MEF2a基因g.47915G＞A/g.47918G＞A位点影响全净膛率，GA基因型个体属于优势基因型个体。通过挑选出与屠宰性状（胸肌率、体重、全净膛重和全净膛率）有关联的MyoG基因g.1131C＞T/g.2204G＞A位点与MEF2a基因g.47915G＞A/g.47918G＞A进行聚合效应分析，结果显示，聚合后的8种聚合基因型个体的全净膛率，在各基因型间无显著差异（P＞0.05），TTGAGA基因型的平均值最高，其次为CCGGGA基因型；其他3个指标各基因型间差异达到了显著，其中体重和全净膛重存在正相关，都是CCGAGA基因型的平均值最高，CTGGGA基因型的平均值次之；CCGGGG基因型的胸肌率平均值最高，其次是CCGGGA基因型。结果显示，单个基因的平均值最高的基因型分别为CC、GG和GA，在两基因聚合后在4个指标中CCGGGA基因型都不是最优的组合，说明两个基因间存在互作效应。【结论】两个基因间存在互作效应，所以用单个基因分子标记进行选育可能会顾此失彼，不能收到良好的效果，但是本研究的聚合优势基因型个体偏少，有待于进一步扩大样本进行验证分析，进行更多基因的聚合效应分析。

The Effect of MyoG and MEF2a Gene Pyramiding on Slaughter Traits of Ducks

【Objective】 The aim of the present study was to explore the polymerization effects of MyoG and MEF2a genes on duck slaughter traits in order to provide a research foundation for further determining the molecular genetic markers related to duck growth traits, also provide a basis of polygene pyramiding breeding of slaughter traits of ducks.【Method】 A total of 240 individuals of Sansui ducks were selected as experimental material in the study, MyoG gene and MEF2a gene were amplificated and had PRC direct sequencing to detect the single nucleotide mutation (SNPs) of all exons of two genes. Base mutation (SNPs) was detected by direct sequencing of the PCR products. GLM statistical model of SPSS 18.0 software was used to analyze the association with different genotypes corresponding to the SNPs MyoG gene and MEF2a gene with Sansui duck slaughter traits. Based on the single gene association analysis results, the polymorphic sites of MyoG and MEF2a genes with significant influence on slaughter traits were employed to build polymerization genotype by using software PHASE 2.0. 【Result】The result showed that eight SNPs were found in MyoG gene and MEF2a gene, and six SNPs were found in MyoG gene and two SNPs were found in MEF2a gene. In all mutations, the G/C mutation in the g.2977G＞C SNP of MyoG gene resulted in the change of codon from GAG to GAC, and the coding amino acid changed from Glu to Asp; While 2 polymorphic site in the MEF2a gene, the G/A mutation at the g.47915G＞A SNP and the G/A mutation at the g.47918G＞A SNP led to codon change from GAA to AAA and GAT to AAT, and the coding amino acid from Glu/Lys and Asp/Asn. The other five SNPs belonged to synonymous mutations, which did not cause the variation of encoding amino acids. Besides, the SNPs fit with Hardy-Weinberg equilibrium except that g.1131C＞T of MyoG and g.47915G＞A, g.47918G＞A of MEF2a gene which were tested by ?2. The results of correlation analysis between polymorphism sites and slaughter traits showed that the SNP of g.1131C＞T and the SNP of g.2204G＞A in MyoG gene had significant influence over the breast muscle percentage, the body weight and eviscerated weight, and the correspondings to homezygote genotype CC and GG were dominant genotypes. The SNP of g.47915G＞A and g.47918G＞A in MEF2a gene affected the eviscerated weight, and the GA genotype individuals belong to dominant genotype individuals. The g.1131C＞T and g.2204G＞A in MyoG gene and g.47915G＞A and g.47918G＞A in MEF2a gene, which relating to slaughter traits (body weight, eviscerated weight, breast muscle rate and eviscerated rate) were selected and the multiple gene polymerizations (interaction) were analyzed, the results showed that after polymerization, the eviscerated rate of eight kinds of aggregated genotype individuals were not significantly different among different genotypes, the mean value of TTGAGA genotype was the highest, followed by CCGGGA genotype. The differences of other three indexes among different genotypes reached a significant level, and weight and eviscerated weight were positively correlated, and the CCGAGA genotype was the highest, followed by CTGGGA genotype; The average rate of chest muscle of CCGGGG genotype was the highest, followed by CCGGGA genotype. The result indicated that the highest main value of genotype of single gene was CC, GG and GA. After two genes combined, CCGGGA genotype in the four indicators was not the optional combination, which showed that there exist interactive effect between MyoG gene and MEF2a gene.【Conclusion】The results revealed that one single molecular marker breeding maybe not good and cannot obtain good result from the interaction of two genes. However, regnant aggregated genotype individuals was not more than enough, more samples should be selected to investigate the aggregated effect of more genes in further study, and to obtain effective molecular markers for poultry breeding.