If someone else laughs out loud at a joke that another person does not find funny at all, then maybe it is because of a difference in their genes. A recent study claims that a variant gene is responsible for controlling how people react to certain situations that require a display of emotions.

The team of researchers found that people who possess a genetic variant of the gene 5-HTTLPR in their DNA sequences are far more sensitive to differing levels of emotions, whether negative or positive. The 5-HTTLPR gene is known to regulate levels of serotonin in the body.

In an attempt to study whether humor is determined by genes or if it is a learned trait that develops over time, the researchers conducted three experiments at the University of California, Berkeley, campus. During the study, the lead study authors, Claudia M. Haase and Ursula Beermann, checked for “crow's feet” markings around people's eyes when they laugh, to distinguish the real smiles from fake ones.

With three experiments conducted over a subject population of 336 participants, the researchers found that people with a short allele -- or variant -- of a 5-HTTLPR gene showed positive responses and expressions to humor. The researchers concluded that participants with short allele had a more genuine smile and laugh than people who had a long allele of the gene. The results remained the same even after taking into consideration other factors, including age, sex, gender and ethnicity.

"Instead, the short allele amplifies emotional reactions to both good and bad environments. People with short alleles may flourish in a positive environment and suffer in a negative one, while people with long alleles are less sensitive to environmental conditions," said Haase, in a statement.

The complete study has been published in the journal Emotion.