The popular depiction of identical twins is that they are exactly that – individuals from a single zygote that are identical because their DNA is identical. But new research has shown that there can be a surprisingly large amount of mutations that differentiate one twin from another.
Twin studies have been popular in identifying the genetic basis of traits and conditions, such as vulnerabilities to disease, as well as in psychological studies examining the effects of genetic “nature” versus environmental “nurture”.
Sequencing the DNA of 387 pairs of identical twins, along with their parents, children and spouses, scientists in Iceland were able to find small numbers of early mutations between twins.Identical twins have an average of about 5.2 mutations between them, but in 15%, there were as many as 100 mutations. Such a number of genetic mutations could influence height differences or susceptibility to cancer.
Jan Dumanski, a geneticist at Uppsala University in Sweden, who was not involved in the new paper, said of the results, “The implication is that we have to be very careful when we are using twins as a model” for discerning the influences of nature and nurture.
The study went beyond previous ones that had already discovered small mutations between twins, to include parents, spouses and children, enabling them to pinpoint mutations in two kinds of cell: those present in just one individual and those passed on to their children. In addition, they found mutations occuring before the zygote split into two embryos.
Study co-author Kari Stefansson, a geneticist at the University of Iceland and the company deCODE genetics, said that his team had discovered cases where pairs of twins had mutations that were present in all cells of one twin, but not found in the other twin at all. However, “sometimes the second twin may show the mutation in some cells, but not all cells,” he said.
Source: Medical Express
Journal information: Hakon Jonsson et al. Differences between germline genomes of monozygotic twins, Nature Genetics (2021). DOI: 10.1038/s41588-020-00755-1
