Characteristics passed between generations are not decided solely by DNA, but can be brought about by other material in cells, new research shows. Scientists studied proteins found in cells, known as histones, which are not part of the genetic code, but act as spools around which DNA is wound. Histones are known to control whether or not genes are switched on. Researchers found that naturally occurring changes to these proteins, which affect how they control genes, can be sustained from one generation to the next and so influence which traits are passed on. The finding demonstrates for the first time that DNA is not solely responsible for how characteristics are inherited. It paves the way for research into how and when this method of inheritance occurs in nature, and if it is linked to particular traits or health conditions. It may also inform research into whether changes to the histone proteins that are caused by environmental conditions -- such as stress or diet -- can influence the function of genes passed on to offspring. The research confirms a long-held expectation among scientists that genes could be controlled across generations by such changes. However, it remains to be seen how common the process is, researchers say. Scientists tested the theory by carrying out experiments in a yeast with similar gene control mechanisms to human cells. They introduced changes to a histone protein, mimicking those that occur naturally, causing it to switch off nearby genes. The effect was inherited by subsequent generations of yeast cells. The study, published in Science, was supported by the Wellcome Trust and the EC EpiGeneSys Network.
That description of changes in histones is not *quite* correct. While histones can be chemically modified to bind the DNA wrapped around them more tightly, maintaining that DNA in an inactive state, that is not the determinant of which DNA is turned off. Essentially, the “decision” to turn off certain DNA expression is made by other proteins in the cell, and influenced by signals that often come from outside the cell. In order for a cell to duplicate its DNA in preparation for replication, it has to remove the histones from the DNA in order for DNA synthesis to occur. This fact alone suggests strongly that the modification state of histones is not heritable, but is a function of various other proteins in the cell.
The DNA undergoes methylation at certain nucleotides. Those methylation patterns are really what control whether a particular stretch of DNA is inert or active. As far as I know, the DNA methylation patterns are heritable, to a degree.
Goodness, even though I looked extensively at regulation of DNA transcription during my PhD studies, I realize now that I am horribly rusty on the whole topic of histone and DNA modification.