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Scientists decode human genes’ instruction manual

Almost a decade after the human genome project lay bare the building blocks of life, scientists have figured out how they work together to create a living person.

The genome project identified about 25,000 genes that are needed to make a healthy human being, but said nothing about how they combine to produce everything from hearts and minds to legs and livers.

Now researchers in California have published what is effectively the first manual to show how genes are orchestrated inside cells — a milestone that promises to revolutionize scientists’ understanding of human development and how it can sometimes go wrong.

Many scientists believe the work will lead to new treatments for life-threatening diseases such as cancer, and possibly mental disorders such as schizophrenia.

The work is expected to shed light on studies that suggest how we live today can have striking repercussions for the health and behavior of our grandchildren. In one study, scientists found that people who smoked as youngsters went on to have grandchildren who reached puberty early. In another, a person’s diet appeared to affect the way their grandchildren burned food.

Scientists have long known that nearly all the cells in the body have the same genetic makeup. What makes a heart cell different from a brain cell comes down to which genes are turned on or off inside it. The process is controlled by chemical switches that stick on to genes and alter how active they are.

For a decade, scientists have been trying to decipher what they call the human “epigenome,” or the pattern of chemical switches in all 200 types of human cell. The prefix “epi” means “on,” because the chemical switches stick on to genes. Until now, they had only a vague idea of what the epigenome looks like.

A team led by Joseph Ecker at the Salk Institute in La Jolla, California, studied human skin and stem cells to produce the first complete map of the human epigenome.
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