Sequence is not everything

dna by mira66

IBM’s “DNA Transistor” Could Sequence Genomes on the Cheap
[Via Discover Magazine ]

When the Human Genome Project finished sequencing the first human genome earlier this decade, the price tag for the endeavor had reached almost $3 billion. Now, IBM has announced details of its effort to bring the cost of sequencing a person’s genome down to below $1,000–and the company says it could go as low as $100. While IBM is hardly the only company racing towards these goals, the company’s chip-based approach makes it a serious contender.

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The discussion of course leads into the worries that knowing the DNA sequence determines a person’s entire life. So if the insurance companies know what your genetic background is, they will know what diseases you are going to get, etc.

This displays a very simplistic view of how our bodies work. There are many other factors that have an impact on many complex diseases that will greatly complicate the picture. Simply knowing the sequence will not be enough.

This can easily be seen by the fact that every cell in the body has the same genetic sequence but there are a huge variety of cells. They are all formed by differential expression of the genetic sequence.

Genes very seldom do anything by themselves. It is the RNA molecules that produce the proteins that do things. Sometimes the RNA itself is responsible for an effect. These products can have altered expression levels that influence the body. They can also have very different forms, depending on the circumstances.

In addition, there are continuing discovery of epigentic factors that control the expression of genes and their products. Methylation is one instance. Alternative splicing is another. I have written about the possibility that modified histones (which act as structural anchors for the genetic material) could have an effect on the entire process of gene expression.

Some of these epigenetic effects can be inherited., increasing the complexity of the matter.

Knowing someone’s genomic sequence is a helpful tool and can be used to help understand some thing but we are much more complex than a string of letters and this complexity may well be revealed when we actually get a process for $100 sequences.

(Of course, that result had better be very, very accurate. There are 3 billion bases in the human genome and even an error rate of 1 in 10,000 would mean that there would be 300,000 errors. This could have substantial ramifications if the error is in a vital gene.)

I tend to think that a major area where $100 genomes will be used will be to actually sequence the expressed RNAs in particular cells. It is relatively easy to convert the RNA to DNA for sequencing. Being able to then get a handle on the exact sequences being used in specific cells, and their amounts, would be very useful indeed.