DNA Sequence Technology
Exciting scientific advances in DNA sequencing technology in recent years have made the DNA sequencing of entire genome practical. Researchers first focused on microorganism with relatively small genomes, on the order of a few million nucleotide base-pairs (Mb). In general, about half of the genes prove to have a known function. What the other half of the genes are doing is a complete mystery.
The first eukaryotic genomes to be sequenced in their entirety were the microbes brewer’s yeast Saccharomyces cerevisiae (13 Mb) and the malarial Plasmodium parasite (30 Mb). The first animal to have its DNA completely read was the nematode C. elegans (100 Mb) in December 1998, followed by the fruit fly Drosophila (120 Mb) and the mouse (300 Mb). The plants Arabidopsis (100 Mb) and rice (430 Mb) were completed in the year 2001.
One of the most surprising results revealed by these genome sequences has been the discovery of just how similar living things are to one another at the genetic level. Forty-two percent of the genes discovered in C. elegans had some sort of match to genes in other organisms only distantly related. Fully 83% of Drosophila genes match those of other species. The matches are not perfect however-the DNA sequences of genes that do the same job have drifted apart over millions of years. But functionality is maintained. For example, when a gene involved in aye development in mice was substituted for its homologue in Drosophila, the flies were born with normal, functional eyes.
