Bombyx mori, the domesticated silkworm, is a major insect model for research, and the first lepidopteran
for which draft genome sequences became available in 2004. Two independent data sets from wholegenome
shotgun sequencing were merged and assembled together with newly obtained fosmid- and
BAC-end sequences. The remarkably improved new assembly is presented here. The 8.5-fold sequence
coverage of an estimated 432 Mb genome was assembled into scaffolds with an N50 size ofw3.7 Mb; the
largest scaffold was 14.5 million base pairs. With help of a high-density SNP linkage map, we anchored
87% of the scaffold sequences to all 28 chromosomes. A particular feature was the high repetitive
sequence content estimated to be 43.6% and that consisted mainly of transposable elements. We predicted
14,623 gene models based on a GLEAN-based algorithm, a more accurate prediction than the
previous gene models for this species. Over three thousand silkworm genes have no homologs in other
insect or vertebrate genomes. Some insights into gene evolution and into characteristic biological
processes are presented here and in other papers in this issue. The massive silk production correlates
with the existence of specific tRNA clusters, and of several sericin genes assembled in a cluster. The
silkworm’s adaptation to feeding on mulberry leaves, which contain toxic alkaloids, is likely linked to the
presence of new-type sucrase genes, apparently acquired from bacteria. The silkworm genome also
revealed the cascade of genes involved in the juvenile hormone biosynthesis pathway, and a large
number of cuticular protein genes.