31 December 2004

Reading Life's Blueprints

The genomes of more than 180 organisms have been sequenced.

Almost every creature carries in its cells a blueprint, encoded in long molecules of DNA. This information enables the organism to build and operate itself.

Every (sexually reproducing) organism is potentially unique, different from even its parents in the specifics of many of its genes, the elements of its DNA instructions.

Scientists currently believe that all Earth organisms had a common ancestor some 3.8 billion years ago. But since then lines of descent have diverged. The more distantly related any organisms are the more differences there will be in their genes.

There are several reasons researchers have been working to learn the complete sequence of all the genetic information (the"genome") of many different organisms include:
  • Interest in learning how different the genes of different organisms are, and thus how those organisms might be related,
  • to learn the vulnerabilities of pathogens (many bacteria and some fungi), parasites (like Plasmodium), and disease vectors (like mosquitoes) so we can prevent or cure the diseases they cause,
  • to learn more about important economic organisms such as yeast, rice, and honeybees so we can breed improved varieties,
  • to have more data on the genes of important laboratory organsims, such as fruit flies, molds, mice, rats, Caenorhabditis and Arabidopsis,
  • to study the history of evolution that is written in our genes.
Of the more than 180 organisms that have had the entire sequence of the DNA in their genomes worked out, most are bacteria and similar organisms with small genomes and simple sturctures. But about 36 eukaryotic species have been sequenced.


Eukaryotes are the more complex cellular organisms that have a nucleus where most of the DNA is organized, a cytoskeleton of protein fibers and tubules, and specialized organelles such as mitochondria. There are currently thought to be about 60 lineages of Eukaryotes. They are divided into about 10 "kingdoms" at present. (Remember when there were only three kingdoms – animals, plants, and protists? Then you are almost as old as I am!)

Most of the life forms people are familiar with are eukaryotes, including the major branches of the "tree of life" such as animals, fungi, and green plants. Some equally fundamental but less familiar branches are the red algae, the alveolates, the stramenopiles, and a grab-bag of groups of organisms called protists. In all there are thought to be about 80 patterns of organization of eukaryotes, organized into about 60 lineages, of which the six just mentioned are the best known.

The 36 eukaryotes for which we now have complete genetic sequences include:
  • Four alveolate protozoans
  • One microsporidial protozoan
  • One other type of protozoan
  • One stramenopile (a diatom)
  • One red alga
  • Three green plants
  • Eleven fungi
  • Fourteen animals, of which
  • Three insects
  • Two roundworms
  • One tunicate
  • Two fish
  • One bird
  • Five mammals
The complete list, as of this writing, is in the associated table.

Here are some useful sites:
A Quick Guide to Sequenced Genomes
Complete List of Sequenced Organisms
Genomes OnLine Database lists ongoing sequencing projects
Entrez at NCBI has everything you could want to know about gene sequences
At The Tree of Life you can learn about different organisms and how they are related

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