Scientists have long suspected that such genetic benefits might accrue from having an extra chromosome 21.

科学家更深入地推测，这些基因上的益处也许能在那条额外的21号染色体上获得增加。

youdao

I owe my ability to accept maternal failure to my son Adam. Though I bred young, never smoked or drank, ate right, and all that, Adam showed up with an extra chromosome, mentally retarded.

我自己获得接受失败的能力还要归功于我的儿子Adam。虽然我很早就生下了Adam。自己也从不吸烟喝酒，饮食正确。

youdao

I'm sensitive, creative and artistic, and perhaps that comes from my extra X chromosome.

我有同情心、有创造力、有艺术气质，或许这正是那条多出的X染色体赋予我的。

youdao

But some people are born with an extra copy of the twenty-first chromosome.

VOA: special.2009.09.09

Occasionally, the extra chromosome doesn't appear until early in the development of the embryo.

CNN: Triple X syndrome

It's also referred to as 47, XXX syndrome because of the existence of a 47th chromosome, which is the extra X chromosome.

CNN: Triple X syndrome

Because only some cells contain the extra X chromosome, females with the mosaic form of triple X syndrome may have less severe symptoms.

CNN: Triple X syndrome