Objective To detect human chromosome 21 rapidly.

目的探索快速检测21号染色体的方法。

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And a gene called KCNJ6, located on chromosome 21, is known to make GIRKs.

而叫做KCNJ6的基因，被发现在染色体21上，已知会产生GIRKs。

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Often, the error resulted in an extra copy of chromosome 21, which causes Down's syndrome.

通常情况下，错误导致21号染色体的多余复制，引发唐氏综合症。

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Fetuses with Down syndrome have three, rather than two, copies of chromosome 21.

WSJ: New Prenatal Tests Offer Safer, Early Screenings

Scientists figured that screens could detect an affected fetus by measuring the presence of elevated amounts of chromosome 21 sequences relative to other chromosomes.

WSJ: New Prenatal Tests Offer Safer, Early Screenings