Researchers conducted three studies to determine genetic variations causing smoking behavior in people, as to how much they smoked and their ability to quit.

For the study, they analyzed DNA profiles of over 140,000 smokers and non-smokers from Europe.

Data was based on a 2008-report connecting a specific region of the human genome--set of 23 chromosomes--to smoking behavior.

One study conducted by University of North Carolina researchers revealed that a single-letter mutation called single nucleotide polymorphisms (SNPs) in DNA code of chromosome 11 was linked to beginning of six percent of smoking behavior.

The mutation on chromosome 9 was associated with 12 percent of quitting behavior, according to researchers.

Second study conducted by scientists at deCODE Genetics found that avid smokers carried certain gene-variants on chromosome eight and 19.

They were the ones puffing about half an extra cigarette per day and at 10 percent higher risk of lung-cancer [abnormal cells that divide without control, which can invade nearby tissues or spread through the bloodstream and lymphatic system to other parts of the body. ] , stated researchers.

The third study by Oxford University was based on discovery made two years earlier by deCODE scientists.

This study confirmed that a gene-variant on chromosome 15 caused nicotine addiction and escalated lung cancer-risk.

Conclusions of the study
Reuters cited Dr. Helena Furberg, University of North Carolina as saying, "This lends support to the idea that smoking is not just a question of will power alone, but that genetics plays a role in how much a person smokes and their ability to quit smoking."

"Our research shows that there is a genetic predisposition to become addicted to nicotine," Stefansson told Reuters.

Stefansson also mentioned that smoking results in nine of 10 lung-cancer cases, however, only a few smokers actually develop the disease.

"Further evidence, that a person's genetic makeup is a factor," added Stefansson.