Researchers have greatly improved upon a technique to assemble genetic sequences from scratch, reaching more than 99% accuracy in assembling the human genome in the correct order. They applied the technique to assemble the genomes of two species of mosquito that spread disease, providing important insights into the ancestry of these species. The advancement will accelerate the genomic analysis of many organisms. Most genomes sequenced today are determined through the generation of short sequenced bits of DNA that are computationally pieced together like a jigsaw puzzle. Hi-C is a sequencing-based approach to piecing these sequences together, ordering and orienting genetic sequences along scaffolding within a chromosome. Given how compact and tightly coiled genetic material is within chromosomes, however, mistakes in genome assembly can easily be made. Here, Olga Dudchenko and colleagues developed a technique to identify positions where a scaffold's long-range contact pattern changes abruptly, hinting that a scaffold has been incorrectly positioned. As well, they developed a novel algorithm to better anchor, order, and orient the sequences. The authors used this modified Hi-C technique to assemble a human genome, finding that 99% of genetic sequences matched a standard reference human genome, and that the orientation was correct for 93% of scaffolds. Next the team used the technique to assemble the genomes of two mosquito species, respectively, that spread disease, Aedes aegypti, a vector for Zika virus, and Culex quinquefasciatus, a vector for West Nile virus. The data shed light on the shared ancestry of these species, which could help scientists better understand ways to control these vectors in the future.