We're all different people and that has a lot to do with our DNA being different. These differences, called single nucleotide polymorphisms
(SNPs), are usually pretty small. Any two unrelated people have about 6 million different SNPs.
A lot of times, SNPs can cause certain people to have certain traits. To look for this, scientists use genome-wide association studies
(GWAS). In these, they compare the DNA from lots of people and look for people who share both a SNP and a trait in common.
So for this study, the researchers first looked at the sleep patterns of more than 4000 people and figured out how much sleep they need each night. They were careful to consider how long people sleep on workdays (when they have to get up at a certain time) and free days (when they can sleep as long as they need).
Then the researchers compared all of these people's DNA. They looked for any SNPs that were common in people who needed less sleep and weren't found in people who needed more sleep. They found that people who shared a certain SNP in their ABCC9 gene only slept for 7.5 hours each night, almost a half an hour or 5% less than others. This ABCC9 gene SNP is found in about 1 in 7 people.
Fruit flies are powerful tools
that scientists use a lot
in genetic experiments.
Of course, just because they all share this SNP does not necessarily mean that it causes them to need less sleep. Scientists need more evidence than that. This is why the researchers in this study did an experiment where they "knocked down" or turned down the ABCC9 gene in fruit flies.
Fruit flies are a really valuable tool that scientists use all the time in genetic experiments. It's relatively easy to add, change or remove their genes, and most of their genes are related to ours. So we can actually learn a lot about ourselves from studying fruit fly genes.
But of course we need to be careful that we don't over interpret the results. Flies and humans are still pretty different from each other, so scientists have to be really careful about any conclusions they make from these kinds of studies.
Flies have two sleep periods every 24 hours, one during the day and one during the night. When their ABCC9 gene (called dSur
in flies) was turned down, the night sleep period was delayed by almost 3 hours, but the day sleep period was not affected.
What does this mean? It suggests that the ABCC9/dSur
gene is involved in controlling nighttime sleep duration, but doesn't cause major changes to circadian rhythm, at least in flies. So it's possible that the SNP that the scientists found in the ABCC9 gene causes people to sleep less every night.
But before we go making any major conclusions, we need to remember two things. (1) Even though flies and humans have related genes, they are still pretty different from each other. And (2) having a small DNA difference in your ABCC9 gene is probably very different from turning down the dSur
gene in flies.