Chromosome 18 Fully Sequenced; Appears to Have Lowest Gene Density of Any Human Chromosome

NEW YORK, Sept. 23 (GenomeWeb News) - The DNA sequence of human chromosome 18 has been completed, and scientists have concluded that the chromosome appears to have the lowest gene density of any human chromosome completed to date -- an average of 4.4 genes per megabase.

In a paper published in this week's issue of Nature, a group of about 55 scientists led by Chad Nusbaum of the Broad Institute of the Massachusetts Institute of Technology and Harvard reported that chromosome 18, around 76 megabases in length, included 337 gene loci. These broke down into 243 known genes, 49 novel genes, 10 novel transcripts, 11 putative genes, 11 "predicted-plus" genes, and 13 gene fragments.

By comparison, chromosome 19, at 55.8 megabases, includes around 1,500 genes, an average of 26.9 genes per megabase.  

The authors noted, however, that despite the low density of genes on chromosome 18, the density of non-protein-coding sequences conserved among mammals was close to the genome-wide average.

The observation that non-coding DNA seems to be evolutionarily conserved across a number of mammalian genomes suggests that there is more to non-coding DNA thanmeets the eye.

"This [observation] has important implications for the nature and roles of non-protein-coding sequence elements," the scientists wrote.