高考英语二轮专题检测精品练习：阅读理解（5）

　　A

　　(2017届·合肥一模)

　　Can people change their skin color without suffering like pop king Michael Jackson？Perhaps yes.Scientists have found the gene that determines skin color.

　　The gene comes in two versions，one of which is found in 99 per cent of Europeans.The other is found in 93 to 100 per cent of Africans，researchers

　　at

　　the

　　Pennsylvania State University report in the latest issue of Science.

　　Scientists have changed the color of a dark­striped zebrafish (斑马鱼) to gold by inserting a version of the pigment (色素) gene into a young fish.As with humans，the skin color of zebrafish is determined by pigment cells，which contain melanin (黑色素)．The number，size and darkness of melanin per pigment cell determine skin color.

　　It appears that，like the golden zebrafish，light­skinned Europeans also have a mutation (变异) in the gene for melanin production.This results in less pigmented skin.

　　However，Keith Cheng，leader of the research team，points out that the mutation is different in human and zebrafish genes.

　　Humans acquired dark skin in Africa about 1.5 million years ago to protect bodies from ultra­violet rays of the sun，which can cause skin cancer.

　　But when modern humans leave Africa to live in northern latitudes，they need more sunlight on their skin to produce vitamin D．So the related gene changes，according to Cheng.

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