 They have difficulty predicting genes with unusual structures, as well as those with a weak translation start signal, weak splice sites or single exon genes.They can incorrectly predict a coding gene model where the gene is a pseudogene and they predict the isoforms of a gene poorly, if at all.The gene models of "C. elegans", "C. briggsae", "C. remanei", and "C. brenneri" genes are manually curated.