Matthew Stanley Meselson (born May 24, 1930) is an American geneticist and molecular biologist whose research was important in showing how DNA replicates, recombines and is repaired in cells. In his mature years, he has been an active chemical and biological weapons activist and consultant. He is married to the medical anthropologist and biological weapons writer Jeanne Guillemin.

Youth and education

He began studying chemistry and graduated from the University of Chicago in 1951. He went on to study under Linus Pauling who assigned him work on x-ray crystallography which he later wrote a thesis on in 1958. He was a research fellow and then Assistant Professor of Physical Chemistry at CalTech until he joined the Harvard faculty in 1960, where he conducts research in molecular genetics and evolution. He started in Harvard as associate professor and taught undergraduate genetics for many years.

DNA breakthroughs

In 1957 with Franklin Stahl he showed that DNA replicates semi-conservatively. The Meselson-Stahl experiment used the Escherichia coli grown in the presence of the nitrogen isotope nitrogen-15, which was then switched to be grown with normal nitrogen, nitrogen-14. When they extracted the DNA using density centrifugation they found three types of DNA, one containing nitrogen-15, one containing nitrogen-14, and a hybrid containing both isotopes. When the hybrid DNA was made single stranded by heating, they could show one parental strand and one that had been newly synthesised, so when DNA is synthesised the DNA double helix splits into two, each of the single strands acting as a template for the synthesis of a complementary strand. This phenomenon is called semi-conservative DNA replication.

He showed in the years that followed many more theories in relation to this with the help of Jean Weigle. In 1961 with Frank Stahl, Sidney Brenner and François Jacob he later demonstrated that ribosomal RNA molecules are stable, which later proved the existence of mRNA - a problem scientists had struggled with previously. He later showed with Charles Radding that genetic recombination results from the splicing of DNA molecules. He also demonstrated the enzymatic basis of a process by which cells recognize and destroy foreign DNA, and discovered methyl-directed mismatch repair, which enables cells to repair mistakes in DNA.

The Meselson effect

The Meselson laboratory studies the evolution of asexuality in bdelloid rotifers. Meselson described the "Meselson effect", in which two alleles in an asexual organism evolve independently and divergently over time, producing what is essentially two genomes in one organism. This is due to the lack of sexual recombination which shuffles genes between alleles during meiosis. Meselson's laboratory provided exciting evidence that this is indeed the case in asexual bdelloid rotifers, and the Meselson effect was subsequently used to explain how bdelloid rotifers deal with dehydration. Dr. Alan Tunnacliffe's Cambridge lab showed that the lea gene had diverged through the Meselson effect into two different genes whose protein products work in synergy to preserve the organism during periods of dehydration, suggesting that the Meselson effect is a mechanism of generating variation that confers evolutionary advantage. 

Chemical and biological weapons disarmament activism

In 1963 Meselson served as a resident consultant in the US Arms Control and Disarmament Agency, since then he has been involved in chemical and biological weapons disarmament policy formation as a consultant and through the Harvard Sussex Program, a disarmament think-tank.

• Meselson was a leader in a 1980s effort attempting to show that "Yellow Rain" was not a Soviet biological warfare agent (as claimed by the CIA and the State Department), but bee droppings, a controversy that remains unresolved.
• In 1992-94, Meselson investigated and reported on the Sverdlovsk anthrax leak, a 1979 bio-warfare mishap in the Soviet Union that resulted in the deaths of 64 persons. Despite his earlier efforts to demonstrate the "innocent" nature of the accident, Meselson's investigation incontrovertably proved that the Soviets had a secret bio-weapons program in violation of the Biological Weapons Convention.

Selected Awards

• 1975 Caltech Distinguished Alumni Award.
• 1995 Genetics Society of America - Thomas Hunt Morgan Medal for lifetime contributions.
• 2002 American Society for Cell Biology’s Public Service Award for Advancing Prevention of Chemical and Biological Weapons.
• 2004 Lasker Award for Special Achievement in Medical Science. The prize honors a lifetime of solving fundamental biological problems.
• 2005 Election as Honorary Life Member to the National Academy of Sciences.
• 2008 Mendel Medal of the UK Genetics Society.