| The silkworm (Bombyx mori) is an important economic insect and an ideal model organism for the biology study. Construction of the linkage map of the silkworm will lead to much great progress of molecular biology research of Bombyx mori. Furthermore, it is also an important bridge between basic and applied research in silkworm. However, there have been few studies so far on multi-marker silkworm linkage mapping using the same segregating population, which makes it difficult to integrate different types of molecular linkage map. In addition, Chromosomes of female silkworm are completely linked, but Mapmaker, which was widely used to construct the linkage map, did not consider the species without chromosome exchanges. Based on these, this study was carried out as followed.1 The linkage map was firstly constructed with three molecular markers, RAPD, SSR and AFLP, using Dazao and C108 as parental strains, and 92 individuals from F2 as the segregating population. 101 RAPD, 143 pairs of SSR and 16 groups of AFLP primers were selected or designed, Mapmaker was used to draw the linkage map. The results were as follows:(1) 83 from 101 RAPD primers were selected to amplify polymorphic fragments. Among 143 pairs of SSR primers, 84 were screened from Dazao to amplify polymorphic fragments and 89 from C108. Meanwhile, 10 from 16 groups of AFLP primers were also selected.(2) 27 linkage groups were constructed using 131 markers in a linkage subgroup, which covered 2815.6cM of the genomics of Bombyx mori, the average length of each linkage group was 104.3cM, the maximum distance between two marker was 51.0cM, and the minimum was 7.1 cM. Among the 27 linkage groups, 4 linkage groups contained three molecular markers, which had 64 markers in all and covered 1567.1cM; 5 linkage groups contained two molecular markers, which had 13 markers in all and covered 297.4cM.(3) 30 linkage groups were constructed using 121 markers in b linkage subgroup, which covered 2704.6cM of the genomics of Bombyx mori, the average length of each linkage group was 90.2cM, the maximum distance between two marker was 55.2cM, and the minimum was 11.2cM. Among the 30 linkage groups, 7 linkage groups contained three molecular markers, which had 63 markers in all and covered 1720.8cM; 6 linkage groups contained two molecular markers, which had 14 markers in all and covered 234.6cM.2 To solve the integration problem of a and b linkage subgroups caused by the complete linkage of chromosomes of the female silkworm, this paper explored the intigration methods of a, b linkage subgroups by means of the published SSR linkage map information and SSR markers of linkage group. According to the characteristics that a, b linkage subgroups contained the same SSR markers or the SSR markers located in the identical linkage group, we divided 10 linkage groups of the a, b linkage subgroups obtained by us into three categories, and integrated every category by different methods, at last, we got 10 new linkage groups. The results showed that the marker number and density of the new linkage groups obviously increased, for instance, the marker sites of group 3 compared with a, b linkage subgroups increased 17 and 41, respectively, the average map distances decreased 5.6cM and 15.6cM, respectively, and the minimum map distances decreased 12.5cM and 15.8cM, respectively. However, the results failed to completely integrate the a, b linkage subgroups, presumably because the number of total marker was not very enough.As the completion of silkworm genome fine map, the continuous discovery of new genes and increase in the number of marker, according to our exploration about the integration methods of the a, b linkage subgroups, and combining with bioinformatisc tools, the gene-character-marker linkage relation may be determined, further, the quantitative genes to control the outcome and quality as well as the resistance genes may be located into specific loci and analyzed, these molecular evidence can provide a reliable basis for the silkworm breeding.
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