Why you're not a morning person. (Don't worry, it's not your fault)

Not a morning person? Blame your parents.

A new study out of Germany's Ludwig Maximillians University of Munich reports that a certain gene - called ABCC9 - controls how long a person needs to sleep.

In a survey of more than 4,000 Europeans, scientists determined that those with one variant of the gene needed a shorter amount of shut-eye compared to those with another version. That shorter-sleep gene is linked to heart disease and diabetes.

The gene can also be found in fruit flies, giving scientists a better understanding of the evolution of sleep habits.

Dr. Mark Mahowald, medical director of the Minnesota Regional SleepDisorders Center, told ABC News the study is an eye-opener: "Sleep duration is genetically determined and not a sign of a defect," he said.