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正常人体细胞有46个染色体,其中22对常染色体,另外2个是性染色体。核型分析常可见有染色体数目增多或减少,当存在有多一个额外的染色体数目时称为三体,此可能由于减数分裂的错误,产生一个具有24个染色体的雌配子,或者是合子第一次有丝分裂有错误。当此种染色体异常仅发生在部分细胞时称之为三体嵌合体。8三体是每个细胞中都有一个额外的第8号染色体,其核型表示为47xy+8。如果除了有此种三体细胞外,还有正常核型的细胞,此个体就是8三体嵌合体,其核型表示为46xy/47xy+8。8三体嵌合体的个体有十分相似的临床表
Normal human cells have 46 chromosomes, of which 22 pairs of autosomes, the other two are sex chromosomes. Karyotyping often shows an increase or decrease in the number of chromosomes, termed as trisomy when there is an extra chromosome number, which may result in a 24-chromosome female gamete due to meiosis or a zygote A mitosis is wrong. When this chromosomal abnormality occurs only in part of the cells called trisomy. The trisomy 8 has an extra chromosome 8 in each cell, with a karyotype of 47xy + 8. If, in addition to such trisomy cells, there are cells of normal karyotype, the individual is trisomy 8 and the individual whose karyotype is 46xy / 47xy + 8.8 trisomy has a very similar clinical table