Study On Construction Of The Linkage Map Using AFLP Marker And Loacation Of QTL Controlling The Whole Cocoon Weight And Cocoon Shell Weight In Silkworm

The whole cocoon weight and cocoon shell weight deciding the output and quality of silk have important economic properties in Silk industry. It is of great importance to study the genes which control such important economic properties. The locating of these genes as well as studies in gene number and their mutual influence will provide a base for the improvement of silkworm species by using molecular marker. In this way, researchers can find out dynamic law of the genes in relation to molecular markers, and manipulate the polygene controlling important traits. So that they can improve breed through Marker assisted selection. On the other hand, the utilizing of coloured cocoon , especially green cocoon which has nature coloring in silk, has great foreground. So it is necessary to obtain the molecular markers which are closely linked to the green cocoon gene, Gc, and locate the Gc, to improve the green cocoon line of silkworm in a relative short period.In the paper, we used Dazao and C100 which have difference in genetic background as parents. 44 individuals were selected randomly from their BC1 (C100(?) ×(Dazao×C100) (?))generation. The Whole Cocoon Weight and Cocoon Shell Weigh of each individual were surveyed. Then we constructed a linkage map with high density and tried to locate QTL in relation to the whole cocoon weight and cocoon shell weight. The main results were as follows.1 The character of AFLP markers in silkwormTotal 8522 identified loci were amplified through 96 primer pairs in 44 progenies.There were 5204 loci with polymorphisim. 1744 had the segregation ratio of 1:1 which are in accordance with Mendel's segregation rules. All the AFLP markers examined appeared to display dominant segregation patterns as RAPD. The number of total loci, polymorphic loci and loci fitting for 1:1 showed greatly difference when different primers were used, for selective base pairs were different.2 A compare of maps with different number of markersWe have constructed respectively the linkage maps with 660 markers,699 markers and 759 markers according to the ratio of 1 to 1 for BC| in silkworm. These linkage maps were compared. First, if the number of molecular markers had increased, the number of linkage group also added, Second if the number of molecular markers had increased, the number of molecular markers in linkage groups and total distance and distance on average all augmented. The average distance of map with 759 AFLP markers was the biggest, but the distance among linkage maps was distributed equally. With the increase of molecular markers, the loci linked also increased, but the biggest distance between two makers decreased. The biggest distance was 74.1 cM in the maps with 699 markers and 759 markers. In a word, the map with 759 markers covered the whole genome of B.mori and corresponded with requirement of QTLs. So we chose 759 markers to map.3 Constructing a molecular linkage map by using AFLP markers in silkworm759 markers were used to map. The result were as follows.3.1 Map consisting of 33 linkage groups and 558 AFLP markers was constructed. However silkworm has only 28 chromosomes. It meaned that some of the linkage groups should be linked together, but we did not link them together because of the absence of specific markers.3.2 The total length of the 33 linkage groups was 6320.2 cent Morgan (cM), and the average length was 191.5 cM . The distance between markers varied range from 0 cM to 74.1cM, and the average distance was 12.0 cM. The number of markers in each linkage group varied range from 3 to 53, and the average number of loci in a linkage group was 17.3.3 The Gc was located between the markers L-P8T1-37 and L-P6T4-83 in group27 in the research.. However the Gc is situated in group 15 of classic linkage map, so it was speculated that the relation between linkage group 27 and group 15 of classic linkage map was close.3.4 The length of linkage group showed positive relevance to the number of markers, that was, the more the number of AFLP markers was, the lo...