Every human being is born with a genetic code of 6 billion bases of DNA, which is copied from our parents. Almost all of these bases are copied correctly, however, a small number are not. It is thought that mutations are mainly due to random errors in copying. In the paper published in Science, the researchers showed that many mutations, a much higher number than previously thought, are actually the result of deliberate self-harm by our cells.
They discovered that in humans, one out of every four sperm and one out of every twelve eggs have a new change in DNA when our bodies make eggs or sperm. This change happens when our cells fix self-induced breaks in DNA that are required for their formation. When these breaks occur, the chance of other genetic changes increases hundreds of times.
The study showed how the DNA break-fixing process in cells leads to different outcomes. In males, with each break, there's a higher chance of mutations taking place, and the types of mutations may vary in different parts of the genetic code. Mutations resulting from deliberate DNA breaks disrupt genes and increase the risk of disease, including developmental disorders such as autism.
Dr Anjali Gupta Hinch, corresponding author of the study and Sir Henry Dale and Wellcome-Beit Fellow at NDM’s Centre for Human Genetics, said: 'Our children are at risk of inborn diseases from mutations, therefore it is important to understand what causes them. Our work also helps to understand other diseases arising from mistakes in DNA, such as cancers.'
While exploring new signs of changes in the genetic code, they revealed unexpected processes of DNA break repair in a specific type of cell division. The findings showed that these changes in genetic material happen because of a collection of repair processes that are prone to mistakes. They indicate that the increased genetic diversity that is afforded by sexual reproduction is good for evolution, but it also comes with a risk of more mutations and diseases.
Read the full paper here: https://www.science.org/doi/10.1126/science.adh2531