How do you feel after you've stayed up late to finish schoolwork? Or the day after a slumber party? Scientists now say that your answers to these questions may depend on your genes. Genes are stretches of DNA that work like an instruction manual for our cells. Genes tell our bodies and brains what to do. People have about 40,000 genes, and each gene can have different forms. So, for example, certain forms of some genes make your eyes blue. Other versions of those genes make your eyes brown. In a similar way, new research suggests that a gene called period3 affects how well you function without sleep. The discovery adds to older evidence that period3 helps determine whether you like to stay up late or get up early. The period3 gene comes in two forms: short and long. Everyone has two copies of the gene. So, you may have two longs, two shorts, or one of each. Your particular combination depends on what your parents passed on to you. Scientists from the University of Surrey in England studied 24 people who had either two short or two long copies of period3. Study participants had to stay awake for 40 hours straight. Then, they took tests that measured how quickly they pushed a button when numbers flashed on a screen and how well they could remember lists of numbers. Results showed that the people with the short form of period3 performed much better on these tests than the people with the long form did. In both groups, people performed worst in the early morning. That's the time when truck drivers and other night-shift workers say they have the most trouble concentrating. After the first round of experiments, participants were finally allowed to sleep. People in the group that performed well on the tests took about 18 minutes to nod off. People with the long period3 gene, by contrast, fell asleep in just 8 minutes. They also spent more time in deep sleep. That suggests that people with the long form of the gene need more and deeper sleep to keep their brains working at top form. 小题1:We can know from the passage that genes can not ________.
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