This is a natural outcome of ourimproving knowledge regarding DNA flexibility itself which is no longer seen asa fixed system but one that changes throughout life.
Through items like this it ispossible to capture the ongoing emergence of a vastly more dynamic model forhuman DNA.
It is a revolution inunderstanding that remains invisible to the popular consciousness.
Identical Twins Are Genetically Different, Research Suggests
By Tia Ghose, Sat, 10 Nov,2012
http://ca.news.yahoo.com/identical-twins-genetically-different-research-suggests-161105688.html
The findings, presented Friday (Nov. 9) here at the American Society ofHuman Genetics meeting, may partly explain why one twin gets cancer whileanother stays healthy. The study also suggests that these genetic changes aresurprisingly common.
"It's not as rare as people previously expected," said studypresenter Rui Li, an epidemiologist at
While past studies have looked at genetic changes, or mutations, insperm and eggs, which can be passed on to offspring, very few studies havelooked at somaticmutations.
These mutations, also called copy errors, can occur early in fetaldevelopment, but because they aren't in the sex cells (the X or Y chromosomes)of the fetus, they can't be passed on.
Other studies have shown that chemical modifications, or epigeneticeffects, can change which genes are expressed over the years, one factorthat renders twins not completely identical. Still, other work has shownthat identicaltwins can have different gene mutations, but this study didn'tdetermine how often they occur.
To find out how often these mutations occur in early development, Liand her colleagues studied the genomes of 92 pairs of identical twins andsearched hundreds of thousands of sites in their genomes for differencesbetween twins in base pairs, which are represented by letters that makeup DNA.For instance, one twin may carry an A at one point while another carries a C.The researchers could only detect differences that would occur very early infetal development and would show up in most cells in the body.
They then calculated the frequency with which these mutations occurred.Only two sets of twins had such mutations, which translates to a DNA changeoccurring once for every 10 million to 10 billion bases that are copied everytime a cell divides. While that may seem like a high accuracy rate, cells inthe body divide trillions of times. So that would mean an average twin paircarries 359 genetic differences that occurred early in development.
One limitation of the study is that they could only estimate themutation rate based on blood cells, but some cells in the body divide much morefrequently and so may rack up many more mutations. Other cells, like braincells, don't regenerate much and would probably remain stable.
"Our DNA samples came from blood samples," Li toldLiveScience. "You need to define different rates in differenttissues."
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