DNA Molecule

A schematic of a DNA molecule. (Public Domain image from Wikimedia commons.)

So far I’ve been talking strictly about my results from the genographic project. This project is aimed at clarifying the history of the human species, but this is far from the only way human DNA sequencing is used.

Genographics focuses on mutations that are relatively old and allow us to track the spread of the human species around the planet. There are two other commercial DNA testing services that use a similar method of testing but are focused on slightly different uses. All use y-chromosome and mitochondrial DNA as well as the 22 sets of autosomal chromosomes, and all look for mutations specific to specific groups. But Ancestry.com uses a set of relatively recent mutation that are most useful for finding recent relatives, while 23and me puts more emphasis on testing for genes know to be associated with health conditions. All three are useful adjuncts to conventional genealogical research, especially for those who have hit a “road block” with a known ancestor of unknown background.

But genealogy is far from the only use of DNA analysis. At the other extreme of price and usefulness is whole genome sequencing, where all 23 pairs of chromosomes are sequenced, letter by letter. This is expensive and rarely done, though the price is dropping fast. We are still talking thousands if not tens of thousands of dollars, not something to do for curiosity alone! However, such sequencing may be useful in finding an abnormal gene in a person with a health problem that cannot be pinpointed, and through knowing what the normal gene does even leading to a cure.

A far more common approach to health studies using DNA is based on the fact that many diseases are closely associated with specific genes. Finding such genes may aid in diagnosis, or (if the genes are found in prospective parents) may lead to counseling about the advisability of having children.

I’m running into this right now. There are a couple of variants of the BRCA gene that lead to an increased chance of breast and/or ovarian cancer, especially in relatively young women. I’ve had breast cancer, though at an age where it’s common. My recent (like this month) ovarian cancer has no obvious relationship to that breast cancer, from which I appear to have recovered, and the ovarian cancer was caught early enough (stage 1) that the chemotherapy I’ve been prescribed is mostly precautionary. But could I have a general susceptibility to this class of cancer? If so, would it be worthwhile removing my remaining breast tissue?  This is why genetic counseling should accompany or even precede this type of testing.

Finally, there are all kinds of forensic genetic tests. Like the genealogical tests, these are generally incomplete and depend on markers—regions where the DNA is known to vary markedly among people. I am no expert in these tests, but they have cleared more than one person on death row.

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