Your Genes or Mine, How Different Are We?

For some time, scientists have believed that individual human beings were 99.9% genetically identical. The 0.1% of the genome that was different (approximately 3,000,000 bases of DNA) was comprised of “single nucleotide polymorphisms” (SNPs are alterations of the individual bases of DNA) scattered throughout the genome. It was thought that some of these DNA alterations may in part explain some of the physical differences that exist between two different, but otherwise normal individuals.

In the summer of 2004, two groups of scientists working independently (one led by researchers at Harvard Medical School and Brigham and Women’s Hospital in Boston and the other led by researchers at Cold Spring Harbor Laboratories) called this scientific dogma into question. Their research identified hundreds of regions of the human genome where the number of copies of a particular DNA segment varied from individual to individual. With only a few exceptions, all DNA segments were thought to exist in two copies (one copy inherited from your mother and one copy inherited from your father).

Both studies showed that there are hundreds of regions of the genome that could have more or less than the expected two copies. This alerted scientists to the existence of a larger source of genetic variation than was previously understood, and forced us to speculate on the implications of this discovery.

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