Is it through epigenetics that environment affects our DNA?
The gene–environment story is complex enough, but it has acquired a new twist in recent years with growing evidence that our environment can actually modify our genes – after a fashion.
The modification, epigenetics, is indirect. DNA sequences stay the same, but there are changes to the set of chemical tags that are carried by the genes or the proteins bound to them. These tags, most often simple methyl (CH3) groups, affect gene expression – usually by preventing . Often, the gene affected is itself one that controls another genetic switch or switches. This means that there may be a cascade effect, where one small change leads to larger adjustments in gene expression.
The study of this kind of secondary modification of the genome is known as epigenetics, and the whole set of tags is known as the epigenome. The epigenome is a bit like the personal settings that gradually customise the operating system on a computer.
Most of the changes are ‘reset’ in sperm and egg. In plants, it seems some epigenetic changes can be passed down to the next generation, and scientists have tried to prove that this happens in animals (including humans) too. However, there is only limited evidence.
A group of researchers based at the London School of Hygiene and Tropical Medicine looked at epigenetic effects in mothers and their children in the Gambia, where the rainy season has a big effect on the foods available at different times of the year. In 2014, they published a study suggesting that mothers’ diets before conception – during or outside of the rainy season – may have had an impact on the expression of their children’s DNA. Those babies conceived during the rainy season had more methyl tags on the six genes they studied. However, the consequences of these modifications are not known.Lead image:
Marcin Wichary/Flickr CC BY NC ND