Study: A Person’s DNA Isn’t Always Identical

Posted November 19th, 2012 at 7:48 pm (UTC-4)

DNA structure  (Image: Michael Ströck via Wikimedia Commons)

DNA structure (Image: Michael Ströck via Wikimedia Commons)

Prevailing wisdom holds that every cell in the body contains identical DNA.

But Yale researchers say they examined skin stem cells and found a number of genetic variations in a variety of skin tissue.

The study, published in Nature, could have profound implications for genetic screening.

“We found that humans are made up of a mosaic of cells with different genomes,” said lead author Flora Vaccarino, M.D., from the Yale Child Study Center. “We saw that 30 percent of skin cells harbor copy number variations (CNV), which are segments of DNA that are deleted or duplicated. Previously it was assumed that these variations only occurred in cases of disease, such as cancer. The mosaic that we’ve seen in the skin could also be found in the blood, in the brain, and in other parts of the human body.”

It’s been long believed that all of our cells have the very same DNA sequence.

Other scientists conducting similar genetic research have theorized the DNA sequence of a cell could be modified during the cell’s development – when DNA is copied from a mother cell to a daughter cell.  These many changes to a cell’s original DNA, they say, could affect an entire group of genes.

While it’s difficult for scientists to actually test these theories, the Yale researchers say they have been able to do so for their new study.

To reach their findings, the research team used whole genome sequencing – a genome is a complete set of hereditary information – to study induced pluripotent stem cells (iPS), which are genetically engineered stem cells developed from a mature-differentiated cell.

The team grew cells taken from the inner upper arms of people from two families. For two years, the researchers examined their genetically engineered iPS cell lines, compared them to the original skin cells, and noted any differences between each cell’s DNA.

The team also conducted further experiments to see what might have caused the differences to occur.

While the research in the project outlined in this recent study was limited to finding variations in DNA sequencing within skin cells, the Yale team is continuing its studies to see if these same DNA variations can be found in developing brain cells of animals as well as humans.

Rick Pantaleo
Rick Pantaleo maintains the Science World blog and writes stories for VOA’s web and radio on a variety of science, technology and health topics. He also occasionally appears on various VOA programs to talk about the latest scientific news. Rick joined VOA in 1992 after a 20 year career in commercial broadcasting.

3 responses to “Study: A Person’s DNA Isn’t Always Identical”

  1. This is a really interesting study, in that it may affect forensics in criminal situations.If DNA is taken from an incarcerated suspect at a time after an alleged incident or if a suspect is accused of a crime years after the alleged crime, physical changes in that suspect’s body may dilute the accuracy of a DNA “match”. Probability and other compelling evidence is one thing in a court of law, however, a 99.9% probability is less than 100% accuracy. This is where “beyond a reasonable doubt” can be questioned.
    F/E GSR (Gun shot residue) on a person’s body doesn’t mean that person committed a crime.
    F/E Blood from a “victim” on or “in” a suspect’s body doesn’t mean that person committed a crime.
    I can go on and on but most people don’t want to hear it. It is rare but some people have spent a lifetime in jails and prisons for something they didn’t do. In some cases forensics vindicated them and in other cases they have found evidence of more crimes committed by that same person.
    Kudos to the YALE Researchers.
    This opinion is from a former NYPD police officer. Thanks for reading.

  2. Edward Cherlin says:

    This study only shows variations in the number of copies of certain genes. This does not by itself affect forensics. That would only happen if different cells from an individual had different genes for reasons that we could not understand and control for.

    In fact, there are well-known reasons for specific cells to contain different genes. Two of the best-known and most-studied are infections by retroviruses like HIV that insert their own genomes into specific cell types, and genetic mixing in areas that generate a large number and variety of different antibodies in the immune system.

    This article is not good science reporting. It contains too little fact and too much supposition.

  3. Doug says:

    I would have to agree. There seems to be some information missing in this article particularly related to why the genome is different in these cells. Cellular DNA is sometimes dynamic. It can be effected by external influences particularly related to viral infection. RNA viruses reproduce by inserted DNA into the host genome. Perhaps, as people age, mistakes could cause duplication of some of the genes. We already know that aging causes damage to the epigenome. Why not the genome as well? Although, it may be a good start for future research.