Tracing origin of subcontinent's Parsi population

It was in the Seventh century AD when a small group of Zoroastrians, threatened by Islamic conquest, fled to what is known as Gujarat in modern India. On their arrival, they were confronted by the local ruler Jadi Rana, who sent a glass-full of milk to the immigrants with the underlying message that his kingdom was full to the brim and there was no place to accommodate the newcomers. The Zoroastrians replied by adding a spoon full of sugar in the milk, suggesting they would assimilate with the locals like “sugar in milk”, compelling the king to find out a place for them.

Was the sugar-in-the-milk anecdote, narrated in several documents including the popular Qissa-e-Sanjaan, purely a figment of imagination or it signifying something else? Armed with sophisticated instruments, a group of biologists set out to find an answer by exploring the secrets hidden in the genetic codes of the modern day Parsi men and women, who descended from those immigrants.

This is not the first time the Parsi community was a subject for research to trace back its roots. But previous studies had a limitation. Majority of the Indian Paris were unrepresented in those research.
To fill up the gap, biologists from the Centre for Cellular and Molecular Biology (CCMB), Hyderabad and their colleagues extensively analysed 174 Parsi DNA samples from India and Pakistan. They also compared them with 600-700 years old DNA samples. This is the first time ancient DNA analysis was used in an Indian research.

The 21 ancient samples were excavated from Sanjan dokhama (the tower of silence) in Valsad district of Gujarat in 2004 by bio-archeologists from Deccan College, Pune. An accelerator mass spectrometry dating of the human remains suggest that the burial site belonged to the 14-15th century.

The team investigated whether the current generation of the Parsi community living in India and Pakistan are genetically related amongst themselves as well as with the Iranian population. They also wanted to check if the genetic compositions of the Parsis were affected by mingling with local Indian and Pakistani population in accordance with the sugar-in-the-milk theory.

“We have done extensive analysis using mitochondrial DNA (maternal line), Y-chromosomal (paternal line) and other DNA markers to trace the origin of the Parsi population of the Indian subcontinent. We found they have genetically mingled (ad-mixed) with the Indian population about 1,200 years ago, suggesting that the first Zoroastrian might have arrived India about the same time period,” said Kumarasamy Thangaraj, lead author of this CCMB study.

The study demonstrated Parsis are genetically closer to the ancient Neolithic Iranians, followed by present day West Asian (Iranian and Caucasian) populations. It also gives evidence of sex-specific admixture and prevailing female gene flow from South Asians to the Parsis.

In other words, this means there are genetic evidence for sex-specific directions of the admixture, suggesting the migration was mainly seeded by Parsi men from Iran who settled down with women in the Indian subcontinent. Even the oldest genetic material they studied, dating to about 1400 AD, had 48% South-Asian mitochondrial lineages — or genetic segments exclusively inherited from mothers.

The results are consistent with the historically recorded migration of Parsi populations to South Asia in the seventh century and in agreement with their assimilation into the Indian sub-continent’s population and cultural milieu Like sugar-in-the-milk.

“In addition to reconstructing the population history of Parsis, the study also showed a major impact of population rearrangements in West Asia due to Islamic conquest”, said Gyaneshwer Chaubey, first author and a senior researcher at the Estonian Biocentre, Tartu, Estonia.

Scientists from the Welcome Trust San­ger Institute, UK, Sindh Institute of Urology and Transplantation, Karachi, University of Health Sciences, Lahore and Calcutta University also took part in the study that was published in the journal Genome Biology.

The challenging task of the ancient DNA analysis is one of the critical aspects of the research. For this, the Hyderabad-based laboratory created a clean room which is being illuminated by the ultra violet light constantly to kill all germs. The room is kept in a positive pressure to ensure that nothing goes in and the air circulated inside the room is screened by highly powerful HAPO filters. The CCMB researchers analysed the ancient DNA in such an environment to ensure zero contamination.

Impure DNAs

“The ancient DNAs are broken DNAs with lot of impurities, whose amplifications are not easy. There is no standardised protocol either unlike the modern DNA analysis. We were building this over the last 4-5 years,” Thangaraj told DH.

“The importance of this study is that it has used extremely modern techniques to prove the basis. It should be also noted that historically, the Parsis of both India and Pakistan come from the same original group which landed in Sanjan,” said Shernaz Cama, president, Unesco Parazor Foundation, an organisation that preserve Parsi heritage and identity.

The new study comes almost a decade after a Bengaluru-based company, Avesthagen, decided to create a large database of Parsi genome to understand the disease profile of the community because of which the Parsis were constantly declining in number — 57,264 in 2011 census as against 69,601 in the 2001 and 1,14,000 in 1941.

Avesthagen chief Villoo Morawala Patell said she planned to have 25,000 samples, out of which the database has 4,500 samples at the moment. Early analysis provided some leads on breast cancer, but it is way to go for the company and its partner Harvard Medical School.

"We did a similar study to show that the Parsi population is close to the European ancestry and distinctly separated from the South Asian ancestry. The CCMB scientists approached it from another angle to come out with the same outcome. They did a good work,” Patell told DH.