Genome sequence of lancelet shows how genes quadrupled during vertebrate...( However Rokhsar added a class of a ...),Health

However, Rokhsar added, "a class of a couple thousand genes did not return to a single copy. Those extra copies of genes acquired some function that prevented them from being lost. The vast majority are regulatory genes highly enriched for transcription factors and genes involved in developmental signaling."

Holland, a research biologist at Scripps in the Marine Biology Research Division, is the lead author of a companion paper appearing this week in the July issue of the journal Genome Research that looks at these genes in detail to see how vertebrates have employed old genes for new functions.

"We are finding that today's complicated vertebrate has not invented a lot of new genes to become complicated," she said. "Amphioxus shows us that vertebrates have taken old genes and recombined them, changed their regulation and perhaps changed the gene function."

Such duplication has given humans and other vertebrates a much larger "toolkit" for making various structures that are absent in amphioxus, including cells for pigment and collagen type II-based cartilage, for example.

Putnam noted another interesting finding reinforced by the amphioxus genome: Most creatures have a lot more genetic variation than humans. While two humans typically differ at only one nucleic acid per thousand in the genome, two lancelets differ at one of every 16 nucleic acids.

"Marine invertebrates actually vary about 6 percent, which means that, on average, one of every 16 bases is different, which is pretty remarkable - it's the difference between humans and certain types of apes," Putnam said. "Humans really are a special case, because of the recent out-of-Africa bottleneck and because of the size of our population. There is a lot less variation than in these little wormy guys that live by the millions in shallow water."

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