Friday, January 9, 2009

Origins 2

The first entire genome sequence of an organism was done in 1995 on the bacterium Haemophilus influenzae by the Institute for Genomic Research. This means that the entire DNA of the organism became known. From that time, a great many organisms have been sequenced, including humans.

It also means that these organisms for the first time can be compared on a molecular basis. The DNA is made of atoms arranged in specific orders. These atoms form molecules, which are then arranged in patterns. The patterns then can be compared, organism to organism.

Darwin's theory predicted patterns have changed throughout life just a little bit from one organism to the next. However, the genome sequencing has shown otherwise. In fact, there are areas where intermediate species are absent, both in the fossil record and in the sequences that would represent slow change. This has been reported by the National Center for Biotechnology Information (NCBI), as in the article, "Biological Big Bang Model for the Major Transitions in Evolution" by Eugene Koonin.

For a while it was thought that archaea were ancestors to bacteria, since traces have been found in rocks that are thought to be about 3.8-3.85 billion years old. But when they were sequenced, starting in 1996, it was realized that they were too different to be direct ancestors. So, it was proposed that both archaea and bacteria had a single previous common ancestor, known as LUCA (last unknown common ancestor).

Several scientific teams, using computers, have worked on the composition of what LUCA would have had to be. One paper published in Research in Microbiology by Ouzounis, et al. in 2006 reported that the organism would need between 1006 and 1189 gene families to mathematically satisfy the requirements for producing both archaea and bacteria. If the eukaryotes are considered (see my previous post for description), LUCA would need between 1344 and 1529 families (depending on underlying hypothetical development).

We will see what that means in terms of random chance for the origin of life in coming posts.

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