As we have all been schooled, DNA determines what is inherited. If it isn’t encoded in the genes, it won’t be passed on. Except it is becoming ever more apparent this isn’t completely true. There is another way that characteristics can be passed to the next generations; it’s called epigenetic memory. Or at least it’s called that in a research paper from Martin Howard and Caroline Dean at the John Innes Centre (Norwich, UK) and published in Nature [24 July 2011, paywalled, A Polycomb-based switch underlying quantitative epigenetic memory]. Their research indicates that certain histones, the material that encases and configures the shape of DNA, can position genes to turn them on or off in response to short-term environmental conditions, and that these configurations are not only passed on to new (daughter) cells, the common process of epigenetics, but can also be transmitted through gamete (egg and sperm) cells as a true generational inheritance.
Epigenetics is a relatively new field, one that continually produces surprises for geneticists and biochemists. It tends to provide challenging contradictions to the notion that genetic responses take place over millennia due strictly to DNA mutation and evolutionary pressures. Epigenetics started with showing how responses to immediate environmental conditions such as drought, famine or stress can be incorporated into the development of an organism. Now it’s showing that some of these responses can be carried into genetic inheritance. Put another way, this is a form of genetic response that can occur within a single generation and is not necessarily highly conditioned by the usual factors of evolutionary selection.
The research by Howard and Dean worked with plants that showed a marked degree of response to cold weather – flowering only at exactly the right time and conditions. These plants have a gene, named FLC, that is related to flowering by ‘remembering’ the length of preceding cold seasons. By using mathematical modeling and experimental analysis, they were able to show that FLC is either on or off, and that after a cold period a high proportion of FLC genes are turned off. This condition delays flowering. In this case further testing indicated that the FLC gene was turned off by selective positioning of the histones modified during a cold period. This epigenetic memory can be passed to succeeding generations of the plant.
This is one example of epigenetic modification of genetic properties. There are many others, such as the recent studies showing that methylation of genes (attachment of a methyl group to a cytosine nucleotide) can also result in turning genes on and off in a heritable fashion. For example one study by Meyer and Elbert (University of Konstanz, Germany) indicates that in response to high stress levels in pregnant mothers, methylation of various genes can be carried to the baby and may express itself in a variety of disorders. Economist [21 July 2011 A mother’s stress while she is pregnant can have a long-lasting effect on her children’s genes]
[SciTechStory: Epigenetics and methylation: New DNA bases linked to protein]