An integrated molecular cytogenetic map of Cucumis sativus L. chromosome 2

In this study, eleven fosmid clones and three plasmids containing 45S rDNA, the centromeric satellite repeat Type III and the pericentriomeric repeat CsRP1 sequences respectively were hybridized to cucumber metaphase chromosomes to assign their cytological location on chromosome 2. Moreover, an integrated molecular cytogenetic map of cucumber chromosomes 2 was constructed by fluorescence in situ hybridization (FISH) mapping of 11 fosmid clones together with the cucumber centromere-specific Type III sequence on meiotic pachytene chromosomes. The cytogenetic map was fully integrated with genetic linkage map since each fosmid clone was anchored by a genetically mapped simple sequence repeat marker (SSR). The relationship between the genetic and physical distances along chromosome was analyzed.Recombination was not evenly distributed along the physical length of chromosome 2. Suppression of recombination was found in centromeric and pericentromeric regions. Our results also indicated that the molecular markers composing the linkage map for chromosome 2 provided excellent coverage of the chromosome.Cucumber (Cucumis sativus L., 2n = 2x = 14) is an economically important vegetable crop in the Cucurbitaceae family. The cucumber genome has been sequenced using a novel combination of traditional Sanger and next-generation Illumina GA sequencing technologies [1]. Illumina GA sequencing technology has significantly improved high throughput sequencing efforts at reasonable cost. However, an intrinsic characteristic of the technology is short read lengths (~50 bp), which prevents their direct application for de novo genomic assembly. Within a total of 72.2-fold genome coverage generated for cucumber genome, Sanger reads provided 3.9-fold coverage and Illumina GA reads provided 68.3-fold coverage [1]. The total length of assembled cucumber genome was 243.5 Mb which is 30% smaller compared to cucumber genome size. Of these, only 72.8% of the assembled sequences were anchored onto