The study, which was published in the journal Science, homed in on single cells to investigate their gene activities, rather than pooling hundreds of thousands of cells and working with averages as has been common practice.
Previous studies led researchers to believe that both gene copies (those from the mother and father) are used to the same extent in the cells of the human body, whereas the new Swedish study found that gene activity is much more dynamic and unpredictable.
The results may explain why people get afflicted by a hereditary illness while their relatives remain healthy, or why identical twins don't always look identical, explained study leader Doctor Rickard Sandberg.
"By developing these methods to measure all gene activities from single cells, we see that there is a much more dynamic pattern," he told The Local.
Following the cells individually allowed scientists a closer look at these patterns and what they meant.
"You can follow the dynamics of gene expression of both gene copies as they become active, and contrary to what people expected, not both are active in each cell all the time."
He added that the ability to zoom in on a cell may improve cancer research, as researchers can now monitor the few cells that escape from primary tumours into the blood stream and lymph fluids.
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"Normally you'd have to pool hundreds of thousands, even millions, of cells to find out more," Sandberg explained.
Sandberg undertook the study to satisfy an interest in understanding how genes are regulated in our cells, their uses, and their unique functions.
The research was conducted at the Karolinska Institutet and the Ludwig Institute for Cancer Research and was financed through grants from the European Research Council, the Swedish Research Council, the Swedish Foundation for Strategic Research and the Åke Wiberg Foundation.