The Physical Genome Mapping of Anopheles albimanus Corrected Scaffold Misassemblies and Identified Inter-arm Rearrangements in Genus Anopheles

The genome of the Neotropical malaria vector Anopheles albimanus was sequenced as part of the 16 Anopheles Genomes Project published in 2015. The draft assembly of this species consisted of 204 scaffolds with an N50 scaffold size of 18.1 Mb and a total assembly size of 170.5 Mb. It was among the smallest genomes with the longest scaffolds in the 16 Anopheles species cluster, making An. Albimanus the logical choice for anchoring the genome assembly to chromosomes. In this study, we developed a high-resolution cytogenetic photomap with completely straightened polytene chromosomes from the salivary glands of the mosquito larvae. Based on this photomap, we constructed a chromosome-based genome assembly using fluorescent in situ hybridization of PCR-amplified DNA probes. Our physical mapping, assisted by an ortholog-based bioinformatics approach, identified and corrected 9 misassemblies in 5 large genomic scaffolds. Misassemblies mostly occurred in junctions between contigs. Our comparative analysis of scaffolds with the An. Gambiae genome detected multiple genetic exchanges between pericentromeric regions of chromosomal arms caused by partial-arm translocations. The final map consists of 40 ordered genomic scaffolds and corrected fragments of misassembled scaffolds. The An. Albimanus physical map comprises 98.2% of the total genome assembly and represents the most compete genome map among mosquito species. This study demonstrates that physical mapping is a powerful tool for correcting errors in draft genome assemblies and for creating chromosome-anchored reference genomes.

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