A simple test could soon identify whether difficulty in getting out of bed in the morning is down to genes or pure laziness.
are night owls by nature
Scientists say that some of us are night owls by nature - late to rise and late to go to bed - while others are larks, genetically programmed to wake early.
They have developed a swab test that can identify a person's natural tendency to wake early or late from cells collected from inside the cheek.
Discussions are under way with Boots to develop an over-the-counter version.
It raises the possibility of workers who are repeatedly late being asked by their bosses to take a test to show whether or not they have a genetic excuse. The test was demonstrated by researchers from the School of Medicine at Swansea University on visitors to the Cheltenham Science Festival.
"The novel technique we have developed at Swansea is entirely non-invasive, so we can use it at a public event," explained Dr Sarah Forbes-Robertson, who worked on the project with Dr Adeel Siddiqui and Alison Baird. "Previously you needed to take blood sample. Our technique allows us to get a useable sample just by swabbing the inside of an individual's cheek."
The test can reveal the activity of a number of different genes that control the "natural" pattern of wake and sleep - the circadian rhythm.
One gene, known as Per2, is especially active at around 4am, and is associated with sleeping. Another, known as REV-ERB, seems to work in opposition to Per2, having its peak activity at around 4pm, and is thought to be associated with wakefulness.
Of her own patterns, Dr Forbes Robertson said: "My peak of Per2 - the 'sleep' gene - is at 6am rather than at the usual 4am. So I really do have a genetic excuse for not being able to manage early morning meetings. To get a full and accurate picture of someone's natural circadian rhythm you would need to take samples four hourly over a full day and night, and also look at all the genes involved.
"But by taking samples at 4pm and 5pm to assess the activity of the REV-ERB gene, we will be able to see if patterns of peak gene expression are shifted forwards or back in time from the norm of 4pm. If your peak is earlier than 4pm it would indicate that you are a natural early bird, if you peak later than 5pm then you are more of a night owl."