Abstract
Silk production quantity is the most economically important characteristic of the domesticated silkworm moth, Bombyx mori. It is controlled by multiple loci. The cocoon and silk production quantity of silkworm strains Jingsong and Lan10 have significantly diverged. A backcross population (BC1) was bred using Jingsong and Lan10 as parents to identify quantitative trait loci (QTLs) for silk quality. In this research, a genetic linkage map of the silkworm was constructed using the BC1 mapping population. The map contained 85 sequence-tagged site markers, 80 simple sequence repeat markers, and 16 single nucleotide polymorphisms. A linkage map was constructed from the data, which consisted of 181 markers distributed over 28 expected linkage groups and spans 2147.1 cM in total length. Fourteen QTLs were detected for cocoon filament length, whole cocoon weight, pupae weight, filament weight, and cocoon shell weight. The 14 QTLs were distributed in 5 linkage groups (linkage groups 1, 14, 18, 23 and 25) based on the constructed linkage map. In addition, five QTLs, which had the highest logarithm (base 10) of odds (LOD) values, were located on the first chromosome, three of which located at the same region in linkage group 1. These results represent an important foundation for the map-based cloning of QTLs and marker-assisted selection for improving the silk quality of economically important silkworm strains.
Highlights
The silkworm moth, Bombyx mori L. has been domesticated over the past 5,000 years from the wild progenitor, Bombyx mandarina (Moore) (Xiang, 1991)
More than 400 mutations have been identified in silkworms, and more than 1,000 silkworm strains are maintained as genetic resources (Ito et al, 2009; Meng et al, 2009)
Several linkage maps for B. mori have been constructed based on various molecular marker techniques, including restriction fragment length polymorphism (RFLP) linkage mapping (Shi et al, 1995), random amplification of polymorphic DNA (RAPD) linkage grouping (Promboon et al, 1995; Yasukochi, 1998), amplified fragment length polymorphism (AFLP) frame mapping (Tan et al, 2001; Lu et al, 2004), simple sequence repeat (SSR = microsatellite) linkage mapping (Miao et al, 2005), and single nucleotide polymorphism (SNP) (Yamamoto et al, 2006; Sreekumar et al, 2011)
Summary
The silkworm moth, Bombyx mori L. has been domesticated over the past 5,000 years from the wild progenitor, Bombyx mandarina (Moore) (Xiang, 1991). More than 400 mutations have been identified in silkworms, and more than 1,000 silkworm strains are maintained as genetic resources (Ito et al, 2009; Meng et al, 2009) It is a key model species of the order Lepidoptera, the second largest group of holometabolous insects, which includes many beneficial species and the most destructive agricultural pests. Cocoon quality is very important because it influences sericulture yield and the selection of silkworm lines for silk production Modern techniques such as transgenesis and marker-assisted selection are the most effective ways of improving silk properties and they are applied widely in silk production (Lu et al, 2004). The construction of linkage maps is a fundamental aspect of gene analysis It provides guidelines for marker-assisted selection and map-based cloning. Some maps have relatively low density and could not be used effectively as guides for breeding B. mori
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