We are told that what you are is in the genes, and that it doesn’t matter if your parents kill themselves in the gym, you are not going to inherit their lovely six-pack. However, new research is showing this is not always so, and that a more complex layer of genetic information that can be affected by diet or stress can also be passed on to your children.
This is all happening through epigenetics, which is not to be confused with garden variety genetics. "Genetics in scientific terms is three billion letters in a row – a,t,g, and c – organised in a particular pattern, and that is the code of life," says Prof Adrian Bracken from the Smurfit Institute of Genetics at Trinity College Dublin. "That's a pretty big book, [and] you could look at that as being the hardware for who you are.
“But imagine that three billion letters are now in every cell in your body. How is that all working out, how is that making you? And how are all those different cells doing different things? You have to have a software to run that hardware.
“The hardware is the code, but the body is able to use different parts of that code in different cells. You have to imagine you have 200 different cell types in your body and you have the same code in each one of them. The body is pretty remarkable in that it’s able to read different parts of this code in order to make different types of cells.
“Some genes are in muscle cells and make muscle cells, and of course those genes should be off in brain cells. In brain cells, the genes that are important to be a brain cell are on, and so on and so on. What the body is able to do is put certain marks [on genes], like a highlighter pen.
“Say you have a blue and a pink highlighter. Then, for example, in a muscle cell, muscle genes are highlighted with a blue colour and they’re on, while the brain genes are highlighted with a pink colour and they’re off. But in a brain cell, the pink highlighted genes are on and the blue are off.”
These highlighted bits are known as epigenetic marks and they can be changed by your lifestyle. Diet has been the most widely-studied factor, but epigenetic marks can also be affected by stress, temperature and even exercise.
For example, scientists have found that when a pregnant woman’s diet is not nutritious enough, epigenetic marks set on the developing baby that prepare it for a life of making do with very little food. These marks remain throughout a person’s lifetime, so that if the baby goes on to have a normal, nutritious diet when it grows up, he or she will be at increased risk of obesity, diabetes and cardiovascular disease.
Prof Bracken says there is no doubt that this effect is real. “We do know from studies in mammals and some in humans that the diet of the mother can affect the baby, the marks that are set down in the baby’s cells. We know that from really good studies in mice [and other] model organisms.”
“Some of the actual marks that we’re talking about are on what are called imprinted genes, and these genes seem to affect behaviour, because they’re expressed in the brain, and also metabolism, so they could be linked to some diseases related to metabolism.”
There are also studies in humans, Prof Bracken says, showing that epigenetic marks are different for certain genes in second and third generation children of women who were pregnant during famines, such as during the second World War.
Hold on. Second and third generation? “Remember that while the baby is in the womb it is also developing its egg cells or its sperm for the grandchildren,” Prof Bracken says. “There’s this window of time when [. . .] the mother and her environment, or what she’s experiencing can affect two generations beyond.”
Prof Bracken says that factors such as stress and diet could also affect the epigenetic marks in sperm cells, affecting the father’s contribution to the baby. However, he says there is not much scientific evidence available, as mostly people have been studying mothers.
So how far could the effect go? Could the mother’s experience affect a great grandchild, or even later generations? “I don’t think there’s any evidence for that yet,” Prof Bracken says. “However, supporting it as a possibility, I’ve been really struck by some recent studies coming out in model organisms, ants, fruit flies and worms – I haven’t seen it in mice yet. In all these studies they’ve seen up to 16 generations influenced by something that is completely not in the genetic code.”
“Eventually it wears off. The point is that this is not genetic, it’s not in the DNA code, it’s in these highlighter marks, which are changing depending on the experience of [an ancestor].”
So it might be possible that the effects of the Irish Famine could have affected several generations. “Certainly we can say that they would [have affected] the next generation, and in the case of the mother, the generation after as well,” Prof Bracken says. However, he also mentions we’ll probably have to wait for the next 10 years of research to fully understand the impact of these events, how far they really were passed on and what effects they had.
It will also be interesting to know whether our current diet – far from famine and filled with sugar, salt and fat – could affect the next generations. We do know that childhood obesity is linked to parental obesity, and although many factors contribute to this, both in terms of genes and lifestyle, the setting up of epigenetic marks in the developing baby may be a key contributor.
Until we know for sure, we might as well be on the safe side and hit the gym or engage in regular exercise – there might yet be hope in our children inheriting that six-pack.