Washington, Aug 7 (IANS): Even though trade in ivory has been banned, the poaching of tuskers continues unabated, threatening African elephants.

However, Alfred Roca, assistant professor at the University of Illinois, has found a way to determine where the ivory comes from.

He and his team have sampled elephants at 22 locations in 13 African countries to get sequences of their mitochondrial DNA (mtDNA).

mtDNA is the DNA located in mitochondria, structures within cells that convert the chemical energy from food into a form the cells can use. Most DNA is "nuclear," found in the cell nucleus.

What makes mtDNA a good marker for tracing the origin of ivory is first, that it is transmitted only by females and second, the fact that female elephants do not migrate between herds, the journal Evolutionary Applications reports.

Roca and collaborators wanted to match these fragments to elephants from a specific location.

Nicholas Georgiadis, researcher now at Washington State, used a rifle to shoot a biopsy dart, which would scrape a square cm of skin from the elephant and fall off, according to an Illinois statement.

Georgiadis collected 653 samples that Yasuko Ishida, researcher in Roca's lab, then sequenced and analysed.

She found eight distinct subclades, or subdivisions, of mtDNA - previous research had detected only two to five - seven of which had limited geographical distribution.

Roca and his team combined these results with five earlier trans-national surveys, which allowed them to examine a shorter region of elephant mtDNA in 81 locations in 22 African countries. Among the 101 unique short sequences detected, 62 percent were present in only one country.

More importantly, the geographic information provided by mtDNA was different from the signal provided by nuclear DNA markers used in previous studies.

Nuclear markers distinguished between forest and savanna elephants; the mtDNA marker indicated a precise location. The best method would be to combine both types of markers.

Roca hopes that the method developed in this research will be used by conservationists to determine the provenance of confiscated ivory.

"It is often hard to trace ivory back to where it came from," he said.

"A ship may have left from a certain port in Africa, but that's not necessarily the country where the elephants were poached."