April 13, 2008


A paradigm shift in genetics (Amanda Gefter, 4/13/08, Philadelphia Inquirer)

The more scientists learn about the complex relationships among genes, environment, disease and phenotype, the more they are realizing how restrictive the old biological paradigm is.

"Our understanding of genetics is currently undergoing a paradigm shift," says Melanie Ehrlich, a molecular biologist at the Tulane Cancer Center. "It is now commonly acknowledged among scientists that it is not enough to look to DNA as the sole determinant of heredity."

Ehrlich is referring to the emerging field known as epigenetics. The epigenome is the elaborate chemical switchboard that can turn genes on and off like flipping a light switch. Our genes encode instructions for the building of proteins. On its own, DNA is nothing but an inert biological handbook, but chemicals in each cell actively read and transcribe the instructions, then use them to build our bodies cell by cell. Every cell in your body contains an identical genome, and yet a brain cell is quite different from a skin cell.

How do the differences arise? Because different genes are expressed from one cell to the next. How does a cell know which genes to implement and which to ignore? That set of instructions is contained in the cell's epigenome. Whereas the genome is static - its sequence of base pairs unchanging except in the rare and often detrimental case of a mutation - the epigenome is dynamic, busily deciding which genetic instructions should be put into action and which should be chemically strangled into silence.

Scientists are now learning that the epigenome is highly sensitive to its environment. The food you eat, the air you breathe, and the stress or happiness you feel can actually alter your genetic makeup - not by changing the sequence of your DNA, but by deciding which genes are expressed.

Biologists have long known that our bodies and behaviors are shaped in part by nature and in part by nurture, but the exact link between gene and environment had always been fuzzy. Now, it is coming into focus: The link is the epigenome.

Epigenetics is opening up a whole new window on the nature of disease. Many cancers, for instance, are not genetic in origin - caused by one or more mutations to our DNA - but epigenetic. "We finally understand that abnormal epigenetic changes are just as important for cancer formation and development as are genetic mutations," Ehrlich says. "Without epigenetic changes, human cancers would probably be rare." The same is believed to be true for autoimmune diseases, diabetes and depression.

Even more surprising has been the discovery that, like genes themselves, epigenetic effects can be passed down from generation to generation. That was first demonstrated in mammals by Randy Jirtle and colleagues in a groundbreaking experiment in 2000. Jirtle took mice that carried a gene called the agouti gene, which made their fur yellow and rendered them susceptible to particular diseases, and fed them a diet containing so-called methyl groups - molecules that can attach to a gene and block it from being used. The methyl molecules, commonly found in foods such as soy and leafy vegetables, attached to the agouti gene and switched it off.

The real surprise came when the mice became parents. Their offspring were born with the agouti gene still in their DNA but silenced. They had brown fur and were no longer susceptible to the same diseases. The parent mice had passed on not only their DNA, but also the epigenetic switches attached to it.

The moral of the story? What you eat today could affect your children's genes . . . even your grandchildren's.

"What you do now won't affect only you," Jirtle says. "That's not trivial."

We are all designists now.

Posted by Orrin Judd at April 13, 2008 7:26 AM

Yup. And acknowleging yet another layer of complexity for life that supposedly emerged evolved from water and rock is actually yet another bit of scientific evidence that there is a God.

Posted by: JAB at April 13, 2008 12:27 PM

sure you are right, lamarck was right, regardless how much they ridiculed him. have a look here

Posted by: borek123456 at April 13, 2008 3:56 PM