Identical Twins Don't Share 100% of Their DNA
upstart writes in with an IRC submission:
Identical twins don't share 100% of their DNA:
Identical twins form from the same egg and get the same genetic material from their parents - but that doesn't mean they're genetically identical by the time they're born.
That's because so-called identical twins pick up genetic mutations in the womb, as their cells weave new strands of DNA and then split into more and more cells. On average, pairs of twins have genomes that differ by an average of 5.2 mutations that occur early in development, according to a new study.
"One particularly surprising observation is that in many twin pairs, some mutations are carried by nearly all cells in one twin but completely absent in the other," Ziyue Gao, an assistant professor of genetics at the University of Pennsylvania, who was not involved in the research, said in an email.
The study authors estimate that, in about 15% of identical twin pairs, one twin carries a "substantial" number of mutations that the other does not share.
[...] The new study, published Jan. 7 in the journal Nature Genetics, offered this unique snapshot into early development because the authors did some clever detective work using DNA from three generations of people.
[...] For now, the takeaway from the current study is that scientists should not assume that identical twins share 100% identical DNA; such assumptions could lead them to overestimate the influence of the environment, when in reality, a genetic mutation may be the source of a given disease or trait, Stefansson said.
However, "such genomic differences between identical twins are still very rare, on the order of a few differences in 6 billion base pairs," with base pairs being the building blocks of DNA, Gao said. It's unclear how many of these small mutations would result in a functional change that alters how the cell works, and in general, "I doubt these differences will have appreciable contribution to phenotypic [or observable] differences in twin studies," she added.
Journal Reference:
Hakon Jonsson, Erna Magnusdottir, Hannes P. Eggertsson, et al. Differences between germline genomes of monozygotic twins, Nature Genetics (DOI: 10.1038/s41588-020-00755-1)
Read more of this story at SoylentNews.