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Judge Rules Against Novel DNA Test In One Twin's Rape Case

A defendant charged with aggravated rape and robbery of two Dorchester women has won his motion to exclude the results of a novel DNA test from his upcoming trial.

Standard DNA testing of evidence from the crime scene showed a match to both Dwayne McNair, 36, of Dedham, and his identical twin brother.

But the Suffolk County district attorney turned to an advanced technique, which it claims can distinguish one identical twin's DNA from the other's.

As WBUR's David Boeri reported last month:

"Next generation," or "massive parallel," sequencing, as it’s called, enables scientists to map out the genome of each twin. That's the entire set of genetic instructions in the bundles of DNA — the chromosomes — found in every cell.

The goal is to find mutations, those rare events in the process of cell division that occur while each cell is otherwise faithfully copying some 3 billion letters of genetic code. Inevitably, as with every typist, there's going to be a typo.

That "next generation" test pointed to Dwayne McNair.

But Superior Court Judge Linda Giles has ruled that the technique is not admissible because it has not been replicated or peer reviewed, and is not yet accepted by geneticists.

McNair is in jail and awaiting trial.

As Boeri reported last month, ahead of Giles' ruling:

If the prosecution is denied the use of the new evidence, it will still have the evidence from conventional DNA testing that narrows the suspects to one brother or the other.

With reporting by WBUR's David Boeri

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