Berkeley The newly sequenced genome of a dainty, quill-like sea creature called a lancelet provides the best evidence yet that vertebrates evolved over the past 550 million years through a four-fold duplication of the genes of more primitive ancestors.
The late geneticist Susumu Ohno argued in 1970 that gene duplication was the most important force in the evolution of higher organisms, and Ohno's theory was the basis for original estimates that the human genome must contain up to 100,000 distinct genes.
Instead, the Human Genome Project found that humans today have only 20,000 to 25,000 genes, which means that, if our ancestors' primitive genome doubled and redoubled, most of the duplicate copies of genes must have been lost. An analysis of the lancelet, or amphioxus, genome, being published in the June 19 issue of Nature, shows this to be the case.
"Amphioxus and humans had a common ancestor 550 million years ago, which allows us to use amphioxus as a surrogate for that ancestor in terms of understanding how vertebrate genomes evolved," said Daniel S. Rokhsar, a faculty member in the University of California, Berkeley's Center for Integrative Genomics and program head for computational genomics at the Department of Energy Joint Genome Institute (JGI) in Walnut Creek, Calif. Rokhsar and JGI post-doctoral fellow Nicholas H. Putnam performed the sequencing, assembly and genome-wide analyses of the amphioxus genome and are lead authors of the Nature paper.
"If you compare the 23 chromosomes of humans with the 19 chromosomes of amphioxus, you find that both genomes can be expressed in terms of 17 ancestral pieces. So, we can say with some confidence that 550 million years ago, the common ancestor of amphioxus and humans had 17 chromosomal elements."
JGI post-doctoral fellow Nicholas H. Putnam, along with Rokhsar and a large international group of collaborators from the United States, Japan, the United Ki
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University of California - Berkeley