美國(guó)英語(yǔ)聽(tīng)力80篇3 Lesson59
Genetic Mutation
Physical changes, such as gray hair and small lines on the face, appear as we grow older.
Now, American scientists say such changes may result partly from changes in our genetic material.
They say these genetic mutations increase over time as the cell-division process in our bodies begins to break down.
Researchers from the Scripps Research Institute in La Jolla, California,
reported the findings in the publication Science.
The researchers examined cells from four groups of people:
normal children, adults, very old people and children with a genetic condition called progeria.
Progeria causes the body to grow older at an extremely fast rate.
The researchers used a new technology to examine more than 6,000 genes at once.
They could see which genes were active among people in each age group.
They found that most of the genes kept the same level of activity in youth,middle age and old age.
However,the researchers identified sixty-one genes that speeded up or slowed down with age.
Richard Lerner of the Scripps InstitUte helped organize the study.
Mister Lerner says one-fourth of the sixty-one genes are what he calls quality control genes.
He says they are supposed to prevent cells from dividing if there are mistakes in the genetic material.
If the quality control genes work,then the genetic mutations are stopped immediately.
But sometimes the cells with genetic matatiofis produce new cells with the same mistakes, or worse one.
He says the increasing number of genetic mistakes in the cell-division process may cause signs of aging.
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