文章大意:这是一篇说明文。新的研究表明,蓝眼睛的人有一个共同的祖先。哥本哈根大学的一个研究小组已经追踪到一种发生在6000-10000年前的基因突变,它是造成当今地球上所有蓝眼睛人类眼睛颜色的原因。
New research shows that people with blue eyes have a single, common ancestor. A team at University of Copenhagen tracked down a genetic mutation (基因突变) which took place 6,000 to 10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today.
“Originally, we all had brown eyes,” said Professor Hans Eiberg. “But a genetic mutation affecting the OCA2 gene (基因) in our body resulted in the creation of a switch, which could turn off the ability to produce brown eyes.” The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin (黑色素). It gives colour to our hair, eyes and skin.
The switch does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the eyeball—effectively turning brown eyes to blue. The effect of the switch on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour.
Change in the colour of the eyes from brown to green can all be explained by the amount of melanin in the eyeball, but blue-eyed individuals only have a small degree of change in the amount of melanin in their eyes. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” said Professor Eiberg. “They have all inherited (继承) the same switch at exactly the same spot in their DNA.” Brown eyed individuals, by contrast, have considerable individual change in the area of their DNA that controls melanin production.
The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair colour, baldness, and beauty spots, which neither increases nor reduces a human’s chance of survival. As Professor Eiberg says, “It simply shows that nature is constantly affecting the human gene and tying out different changes as it does so.”
12. What is the finding of Professor Hans Eiberg’s team?
A.The eye color can be changed by adjusing genes today. |
B.Blue-eyed people have survived due to their special genes. |
C.A genetic mutation leads to the change of people’s eye color. |
D.The eye color can help discover where people’s ancestors were. |
13. What can we learn about “the switch” from Paragraph 3?
A.It produces melanin directly. | B.It helps produce less melanin. |
C.It can be limited by other genes. | D.It helps OCA2 function in our body. |
14. Why can we conclude all blue-eyed individuals are linked to the same ancestor?
A.They have more change in gene. | B.They have exactly the same gene. |
C.They have more melanin in their eyes. | D.They have little change in the amount of melanin. |
15. What does the last paragraph want to tell us?
A.Nature affects our genes. | B.Only the fittest can survive. |
C.We are decided by our genes. | D.Some genetic mutations are meaningless. |