By Daniel Hubbard | May 13, 2012
For years now genealogists have been interested in genetics. DNA testing can help us solve genealogical puzzles. It can tell us about unknown relatives. It can give us insight into ethnicity.
Sometimes it proves that there is something wrong in our paper trail. Sometimes it shows that our research in the records is likely to be correct. Other times it simply gives us insight into our past. It might say that we probably have some Native American blood that supports a family story or that somewhere in our past we have an unknown ancestor who hailed from a part of the world that we would never have imagined.
All these types of test result point back to a men and a women producing offspring—those specific children from whom we descend. The children who passed some of their parents’ genes on to us. There is another way that the past can leave its imprint upon our DNA, a way that is not nearly so well known.
One of the standard ways of explaining how DNA works is to compare it to an instruction booklet. As the machinery of the cell reads the DNA, it simply does what the instructions it reads tell it to do. It cannot be quite that simple though. If it were, then every cell in your body would be identical. Some instructions are followed while others are skipped, or at least followed less often. Crudely speaking, there are switches that can turn genes off. Instructions can get crossed off in our booklet. They are still there but it is clear that they should not be followed.
If that was all there was to it, I wouldn’t be writing on the topic. Epigenetic effects are not just important within an individual. There is a region on chromosome 15 that is missing in rare instances. That missing section causes two very different genetic disorders (Angelman syndrome and Prader-Willi syndrome). The names aren’t important. What is striking is that from the point of view of the DNA, these should be identical disorders. The problem in the DNA is identical. Yet something causes one problem in the DNA to lead in two very different directions. If the chromosome with the missing genes comes from the mother, the child develops Angelman syndrome. If it comes from the father, Prader-Willi syndrome is the result. Somehow the genes differ depending on whether they come from the mother or the father, yet their code is identical. Different switches are set depending on whether the chromosome came from the father or the mother.
That is somewhat odd. The same genes (or lack thereof) can behave differently depending on which parent served as he source. It gets stranger.
We have our genetic inheritance. It is whatever it is. Our ancestors make their contributions but those contributions record nothing about the lives they lived. How ever their lives turned out, they lived them with the genes they received from their parents, who received them from their parents.
Sometimes those ancestors passed down their stories and we either are told them or we aren’t. We received their DNA but those stories are the one chance to receive something of the lives they led passed on from family member to family member. Or are they?
There is a third way. Sometimes their story, it seems, can lie within our cells and be passed on generation after generation. Not genetic information they had from the beginning, but the imprints of events in their lives.
At least two studies of extreme changes to the food supply, famine and supreme over abundance, have shown that the amount of food that was available in one generation can leave traces that can be passed down from parents to children. When boys of about eleven or the mothers of unborn girls have little to eat or devour an over-abundance, those boys and girls experience epigenetic changes that they can pass on. Genes’ switches become flipped and those switches can stay flipped for generations. Part of their life story becomes imprinted within, in a way that transcends them and spreads among their descendants. What a great-grandfather experienced as a boy can be seen in his great-grandsons. Generations later, their health is affected.
If a father began to smoke before puberty, there is evidence that his own sons will tend to have an abnormally high body mass index. Animal experiments have shown evidence that epigenetic effects of maternal stress and chemical exposure can last for generations. It seems that not just the genes our ancestors had is part of our legacy. Some of what happened to them and the choices they made are part of the legacy we receive as well.
I wonder if someday it might be possible to take a test that would give us a hint that an ancestor had suffered in a famine, someone in our paternal line smoked when he was eleven or twelve, or someone in our maternal line lived on a farm because we can see that someone back in time was exposed to agricultural chemicals.
The past is within us in ways we are only beginning to learn to imagine.Twitter It!