Ren et al. (2018). Genomic basis of recombination suppression in the hybrid between Caenorhabditis briggsae and C. nigoni. Nucleic Acid Research.

https://academic.oup.com/nar/article/46/3/1295/4793371

The cb4 C. briggsae assembly contains 5,997 gaps (represented by ‘Ns’) and 361 contigs not anchored to any chromosome (‘unassigned’). Ren et al. filled 2,304 gaps by replacing ~240 kbs on six chromosomes and partially closed gaps in ‘unassigned contigs’ and extended ~800 kb sequences. This resulted in a total of ~1,040 kb of new sequence data. The authors also anchored 124 of 361 ‘unassigned’ contigs that added ~1.8 Mb back to individual chromosomes.