For many years scientists thought that a person’s life was spelled out by their genes but today evidence is gathering to suggest that genes can be changed or modified by our lifestyle, our diet and maybe even the lifestyle and diet that our parents had.
This new branch of genetics called ‘epigenetics’ was born just over 20 years ago and is suggesting ways that stress, diet or exposure to environmental factors can alter our genes. Geneticists are coming to believe that DNA isn’t a permanent, unchanging molecule that programmes our lives, it can be fine-tuned by attaching molecules to it to control the way genes are expressed. Put simply, these special molecules can bind to a gene to get it either ignored or enhanced and so, turn it on or off. The most important molecules found so far, are methyl groups, which bind to cytosine in a CG pair in a gene, tagging them so they have new effects. This ‘DNA methylation’ or tagging might turn on genes that cause cells to differentiate into skin cells, or switch off a gene that controls manufacture of insulin. There’s also evidence that certain cancers can be caused by tags that occur in the wrong places or on the wrong genes and switch them on or off so that tumours start to grow. Other research is looking at possible links to autoimmune diseases such as multiple sclerosis.
But it’s not only tags that are important. DNA is wrapped around its own core of histone proteins and the tightness of the coiling can affect how easy it is to read. Epigenetic studies are investigating how this influences transcription and translation of the DNA’s information. Coiling may work rather like a volume control which makes it easier or harder to hear what the DNA is saying. Understanding of both methylation and coiling is providing exciting new evidence that our characteristics really can be tweaked and modified during our lifetimes.
So what affects methylation? Certainly diet may be involved. Folic acid and vitamin B12, which women are encouraged to take during pregnancy, contain methyl groups and are linked to a decrease in incidence of spina bifida, other neurological conditions and asthma. And there is some evidence that a bad diet can interfere with methylation. Other research has suggested that stress or toxins can also be influential, and many other factors are being examined.
As more evidence is collected, we may come to discover that our characteristics are affected, not only by our own lifestyles, but also by those of our parents and even grandparents. Once it was thought that epigenetic tags were deleted before DNA was passed on to the next generation but research has shown that 1 or 2% of the tags remain and can be passed on to children and even grandchildren.
If this exciting new area of biology interests you, you will study it in Topic 7 of the IB course. You may also like to read about the Dutch Hongerwinter study of the famine in the Netherlands in the 1940s which some say affected the DNA of the people there or the research of Waterland and Jirtle (2003) which linked the diet of mice to characteristics of their offspring.