2. 考研
  3. In 1999 when MiShel and Carl Meissner decided to have children, they tackled the next big issue: Should they try to have a girl?

In 1999 when MiShel and Carl Meissner decided to have children, they tackled the next big issue: Should they try to have a girl?

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问题     In 1999 when MiShel and Carl Meissner decided to have children, they tackled the next big issue: Should they try to have a girl? It was no small matter. MiShel’s brother had become blind from a hereditary condition in his early 20s, and the Meissners had learned that the condition is a disorder passed from mothers to sons.  If they had a boy, he would have a 50 per cent chance of having the condition. A girl would be unaffected. The British couple’s inquiries about sex selection led them to Virginia, US, where a new sperm-separation technique, called MicroSort, was experimental at the time. When MiShel became pregnant she gave birth to a daughter. Now they will try to have a second daughter using the same technique.
    The technique separates sperm into two groups—those that carry the X-chromosome (染色体) producing a female baby and those that carry the Y-chromosome producing a male baby.
    The technology was developed in 1990s, but the opening of a laboratory in January 2003 in California marked the company’s first expansion. "We believe the number of people who want this technology is greater than those who have access to it," said Keith L. Blauer, the company’s clinical director.
    This is not only a seemingly effective way to select a child’s gender. It also brings a host of ethical (伦理的) and practical considerations—especially for the majority of families who use the technique for nonmedical reasons.
    The clinic offers sex selection for two purposes: to help couples avoid passing on a sex-linked genetic disease and to allow those who already have a child to "balance" their family by having a baby of the opposite sex.
    Blauer said the company has had an impressive success rate: 91 per cent of the women who become pregnant after sorting for a girl are successful, while 76 per cent who sort for a boy and get pregnant are successful.
    The technique separates sperm based on the fact that the X chromosome is larger than the Y chromosome. A machine is used to distinguish the size differences and sort the sperm accordingly.
The sperm-separation technique is based on the fact that the chromosomes responsible for babies’ sex ______.
选项 A、are of different shapes
B、are of different sizes
C、can be identified
D、can be reproduced
答案B
解析 文章最后一段作者说：分离精子的技术是基于X染色体比Y染色体大。科学家用一种机器把大小不同的染色体分开。
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