Quick! Where would you find the largest number of twins in the world?

Umri.

One out of ten persons born in a sleepy village near Allahabad is a twin.

Now top geneticists have turned their attention on the genetic material (DNA) of the people of Umri to crack the mystery of why they produce the largest number of twins in the world.

The entire village has become geneticists' prized laboratory as there is no place in the world where so many twins are living in one place, scientists of the Centre for Cellular and Molecular Biology in Hyderabad told PTI. 

"It is really a genetic gold mine," says CCMB director Lalji Singh. Out of Umri's 800 residents nearly 120 were born twins, he said. "We actually counted 40 pairs," says Chandak, also of the CCMB.

Two weeks ago, Chandak and Singh collected blood samples of the twins and their parents for analysis of their DNA.

Umri consists of some 200 households, 95 per cent of them belonging to the Muslim community. According to the village elders, people married within the village and almost all deliveries took place at home, as there are no hospitals.

In nature, there is one chance in 80 for a mother to deliver twins and one in 240 for delivering twins that are absolutely identical. 

In Umri, however, one of ten deliveries produced twins. The CCMB team found one family with ten children four of whom were born twins, all girls -- which Singh describes as 'a very rare event'.

The oldest twin met by the team was a 38-year-old suggesting that twinning has been taking place for years.

Identical twins emerge from a single fertilized egg and non-identical twins are born if the woman carried two eggs fertilized simultaneously. Scientists are not sure if twinning is entirely a 'chance' phenomenon and the CCMB study will find out if there is a genetic basis for it and if DNA rearrangement during the embryonic development is responsible.

According to Singh, because of the high rate of inbreeding in Umri, the study might be able to discover the gene (or genes) responsible for twinning, if there is one.

The CCMB studies will go one step further and try to find out the genetic basis for the difference in the behaviour of twins and susceptibility to diseases.  

"Umri is going to open a new chapter in genetic studies," Singh said.