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在正常群体中,额外标记染色体(EMC)的频率约为0.26‰,21三体的频率约为1.25%。这两种染色体异常随机发生在同一家庭的频率应该是很低的。本文报告双亲之一有EMC,子女中有3人为21三体核型的二个家系。Q显带及
In the normal population, the frequency of additional marker chromosomes (EMC) is about 0.26 ‰ and the trisomy 21 frequency is about 1.25%. The frequency of these two chromosomal abnormalities occurring randomly in the same household should be very low. This article reports that one of the parents has EMC and three of the children have two trisomy 21 families. Q-banding and