Research Of Genetic Relationship And Heterosis By RAPD And SSR In Bombyx Mori

Bombyx mori.L is the model insect of Lepidoptera as well as an important commercial being.The traditional means of classification of Bombyx mori is based on morphologic marker,because with its rich variety resources and complicated genetic relationship,it is hard to separate them from each other through genotype.The recent development of DNA molecular marker brings a new method to classify the genetic relationship of silkworm;heterosis is the most important ways to culture better strains,so it is become more and more crucial to find an appropriate way to analyse the effect of hetemsis.Traditional methods assaying combining ability are time-taking and inconvenient, and the results are not so stable and convincible,all of which makes laeterosis restricted to wide use.Thus,to find a fairly reliable method to forecast heterosis is urgent and important for further taking advantage of heterosis of Bombyx mori.L.Molecular marker techniques have being used in many other plants and animals,but haven't in Bombyx mori.In this paper,we studied those problems and got the following results.1 Analysis of DNA polymorphism and genetic relationship of 12 commercial silkworm varieties by molecular marker techniquesWe analyze the DNA polymorphism of 12 commercial silkworm varieties based on PAPD and SSR.21 RAPD primers were used to amplify the genomic DNA,196 distinguishable bands were produced,among which 143 bands showed polymorphism.The percentage of polymorphism was 72.96%.The relative distance value among different races were 0.157-0.352.And 32 SSR primers were used to amplify the genomic DNA,86 distinguishable bands were produced,among which 80 bands showed polymorphism.The percentage of polymorphism was 93.02%.The relative distance value among different races was 0.214-0.600.The two molecular marker techniques have not great differences in specifying silkworm,consisting with traditional methods.The evolutionary distance implied the phylogenetic relationship among different races from molecular level and the result might be useful in cross breeding.2 Effect of different number and variety of markers on genetic relationshipChoose 60,80,100,120,140,160,180,196 markers randomly from the 196 markers we got through RAPD PCR amplification.Analyse genetic distance and relationship between clusters with TREECONW.The result of cluster analysis tends to stabilize when the RAPD markers comes to 160.Choose 46,56,66,76,86 markers randomly from the 86 markers we got through SSR(Simple Sequence Repeat)PCR amplification.Analyse genetic distance and relationship between clusters with TREECONW,too.The result shows that genetic relationship between 12 strains of Bombyx mori tends to stabilize when the SSR markers comes to 56.we also find that fewer markers of SSR technique is enough to analyse precisely than that of RAPD.3 Research of heterosis of Bombyx mori using molecular markersChinese system Jing song,75 xin and Japanese system hao yue,7532 were chosen for complete diallel cross to test six silkworm characters.Then,calculated the heterosis of each character and extracted DNA from parent and F1 hybrid.RAPD and SSR marker were used to get the genetic distance and polymorphism heterosis and the correlation between polymorphism heterosis and character heterosis.(1) The six characters all shows mid-parent heterosis,especially for those with great genetic distance.But hybrid combination are different when refers to different character.(2)In this paper,36 RAPD primers and 43 SSR primers were used to PCR amplification.The bands from PCR amplification were analyzed and the genetic distance of them were calculated and then value the correlation between polymorphism heterosis and character heterosis.Five characters of Bombyx mori show irrelevance to heterosis rate only cocoon weight and genetic distance show negative correlation.The result shows that neither RAPD nor SSR can forecast heterosis of 4 strains'F1.(3) 36 RAPD primers and 43 SSR primers were used to amplify genome DNA of silkworm and F1.The bands from PCR amplification were analyzed and the polymorphism was calculated to estimate the heterosis,then value character heterosis.RAPD molecular markers and SSR molecular markers get similar results that heterosis of three characters can predicted and show significant correlation.Though other three characters and molecular markers show no significant correlation,it is more advanced than molecular markers.Thus,molecular polymorphism marker is a promising technique to forecast heterosis in Bombyx mori.