| The development of agriculture, such as farming and animal husbandry, has proved that selection and use of excellent varieties is one of the effective ways to avoid the recession of growth traits and disease resistance traits. The precise and accurate knowledge of genetic parameters is a prerequisite for making efficient selection strategies in artificial selection programs. In our study, we used different kinds of mating materials to estimate the genetic parameters of growth traits at different development stages. Twenty-three full-sib families were also used for challenge test by Vibrio parahaemolyticus and the survival data were used for genetic analysis of disease resistance in Meretrix meretrix. These results provide a basic genetic evaluation for growth traits and resistance traits. Besides, they would be useful for the design and operation of a practical selective breeding program in the clam M. meretrix. Further more, we developed a breeding database by Access software application based on the breeding data of Meretrix meretrix in recent ten years, which were convenient and efficient for the breeding information management and provided a foundation platform for genetic evaluation and artificial selection. The main results were as follows. 1. Genetic parameter estimation for growth traits in the juvenile stage of Meretrix meretrix.In the study, 23 full-sib families were produced using part factorial design as described by Berg and Henryon. Moreover, genetic parameter of growth traits in the juvenile stage of Meretrix meretrix were estimated using single trait animal model and two traits animal model. The results showed that the estimated heritabilities of shell length and shell height arranged from 0.11 to 0.34 at metamorphosis stage, and the phenotypic and genetic correlations were 0.86~0.95 and 0.97~0.99, respectively. At the age of 5 month, the estimated heritabilities of shell length and shell height arranged from 0.23 to 0.41, and the phenotypic and genetic correlations were 0.85~0.93 and 0.93~0.98, respectively. However, the common environment effects were increased with the age increasing(from 0.02 to 0.38). For example, the common environment effects at the age of 5 months were significantly larger than those at settlement and metamorphosis stage(P<0.01). While the genetic correlations of shell length between different development periods were positive but not significant, the correlation coefficients were different between each other(0.34~0.71). 2. Genetic parameter estimation for growth traits at the age of 1 year Meretrix meretrix.Residual maximum likelihood(REML) and Bayesian inference were used to estimate the genetic parameters of growth traits in Meretrix meretrix based on different mating designs and different sizes of families in factorial mating design. The results showed that the heritability estimates obtained from Bayesian inference were a little smaller than the results from REML. When the same method was used(REML or Bayeisan) to estimate the heritabilities of growth traits from different mating designs, we found that the heritabilities obtained from nested design were medium to high level(REML: 0.41~0.56, Bayesian: 0.36~0.45). While the heritabilities obtained from 3×3 factorial design and the 5×5 factorial design were similar to each other(REML: 0.15~0.22, Bayesian:0.11~0.17). In order to compare different sizes of factorial designs for inference on heritability, we decomposed 5×5 factorial design into one-hundred different 3×3 factorial designs and twenty-five different 4×4 factorial designs. The results showed that the average estimated heritabilities of growth traits obtained from REML and Bayesian were 0.23~0.32 and 0.11~0.12. Genetic and phenotypic correlations among traits were positive and high and had no significant difference between different mating designs and different sizes of factorial designs. Breeding values of growth traits were estimated using REML, and the accuracies of estimated breeding values were compared among different materials. The results showed that the averaged accuracy values from 5×5 factorial design were 6.42~6.57, which were more precise than those from nested design in 2007 when the size of families and the individuals were similar,. For factorial designs, the accuracies of estimated breeding values increased as the number of families increasing. 3. Estimates of genetic parameters of vibrio parahaemolyticus resistance in MeretrixmeretrixVibrio parahaemolyticus has been shown to cause mortality in numerous clam species, among whom is the clam Meretrix meretrix. The aim of our study was to analyze the genetic variation in resistance to vibriosis. The challenge test data comprised 1150 individuals from 23 full-sib families and the experiment was terminated 25 days. The overall survival at the end of the test was 40.17%, and the survival percentage were very different among families, which varied from 8%~66%. Genetic analysis of vibriosis resistance based on survival data during the challenge test were analyzed with three models. When Cross-sectional model was used, the heritability estimates ranged from 0.04~0.29, and Survival score model had similar heritability(0.24±0.05). However, when we used linear model to analyze the day of death, larger heritability was obtained(0.42±0.14). Estimate breeding values from three models showed high and positive correlations(0.91~0.97), which mean that the ability of breeding value prediction was similar among these models. The genetic correlation between growth traits and survival were low and not significant(0.08~0.18), which suggested that the growth traits and resistance against Vibrio parahaemolyticus in Meretrix meretrix could be improved separately. 4. The development of breeding database of the important economic traits in Meretrixmeretrix.We developed a breeding database of the important economic traits in Meretrix meretrix by Access software based on the breeding data in recent ten years. The database contained the basic breeding information, growth traits breeding information, disease resistance breeding information, breeding values information and development situation information. The database was not only convenient for users to query, update and modify the breeding data, but also satisfied the needs of data classification, summary and basic statistical analysis. The database provides a basic platform for genetic evaluation and should be useful for the design and operation of a practical selective breeding program in the clam M. meretrix. |
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