It can apply to characteristics passed from a cell to its daughter cells in cell division and to traits of a whole organism. The letter that is tagged is C or cytosine and when it is modified, or methylated it is called 5-methyl cytosine. So how can we solve the conundrum of how the roundworms inherited the long lived characteristic, without inheriting the DNA sequence that initially caused it?
Water and Cells. Subsequently the same process has been applied to other species and may have medical uses in generating cells that could repair tissues damaged by injury or disease.
It turns out that the genes that were mutated in the worm study make proteins that work together to add a methyl tag to nucleosomes. This development of an unfertilized egg into a male and a fertilized egg into a female is a type of parthenogenesis known as arrhenotokous parthenogenesis.
In fact, research with the Dutch Hunger Winter families continues, and a recent study looking at a gene galled IGF2 found lower levels of the methyl tag in the DNA of this gene in individuals exposed to the famine before birth. They are composed of DNA and proteins and are located within the nucleus of our cells.
First the nucleus the part containing the DNA was removed from the oocyte. In most cases, more methylated Cs in the DNA of a gene results in the gene being switched off. So as the cells divide, the ball of embryonic stem cells gradually develops into all the cell types and structures of the baby at term.
A bit of genetics that most of us know about is what makes a boy a boy, and a girl a girl. Two copies of the same version in a female cat results in ginger or black fur respectively, but one copy of each gives a tortoiseshell effect.
About letters-worth of DNA or base-pairs is wrapped around each nucleosome, and this helps package the 3 billion base pairs of genetic code into each of our cells. The most sensitive period for this effect was the first few months of pregnancy. But what is it about royal jelly that leads a larva that would otherwise grow up to be a worker, to become a queen?
Diagram 2. You can think of these tags as post-it notes that highlight particular genes with information about whether they should be switched on or off. Diagram 3. In the last year of the Second World War in Europe, a food embargo imposed by occupying German forces on the civilian population of the Netherlands resulted in a severe famine, coinciding with a particularly harsh winter.
So epigenetics is about how genes are expressed and used, rather than the DNA sequence of the genes themselves, but how does this work? When the faulty chromosome is inherited from Dad, there is no functional copy of the imprinted genes that are switched off on the maternal chromosome 15 and the result is Angelmann syndrome and vice versa for Prader-Willi syndrome.
We are now in a position to explain this apparently strange result. Diagram 1. This switch is thought to be set up in the gametes eggs and sperm so right from the start, genes received from Mum and those from Dad are labelled differently with epigenetic tags and so are not equivalent.
These new discoveries explain these previous puzzling observations, but also have great potential for new understanding and treatments for human disease.