Assisted reproduction and preimplantation genetic diagnosis (PGD) involve various complicated techniques, each of them with its own problems. However, the greatest problem with PGD for chromosome abnormalities is not of a technical nature but is a biological phenomenon: chromosomal mosaicism in the cleavage stage embryo. Here, we present a hypothetical, quantitative model for the development of chromosomally normal, abnormal and mosaic embryos. The arising of mosaicism in 2-8-cell embryos was described by a binomial probability model on the occurrence of mitotic events inducing chromosomal changes in the blastomeres. This model converted the 'mean' rate of mosaicism found in cross-sectional studies (60%) into an equal rate of mosaic embryos at arrival at the 8-cell stage (59.8%). The disappearance of > 90% of the mosaic embryos or the mosaicism itself from surviving embryos during the morula stage was explained by mitotic arrest of most of the mitotically changed cells under increasing cell cycle control. In our model, 25.9 and 14.3% of the embryos at the 8-cell stage are normal and abnormal respectively. The remaining 59.8% of the embryo shows mosaicism: 34.6% of abnormal/normal cells and 25.2% of abnormal/abnormal cells. The high proportion of abnormal and mosaic embryos together explains the high rate of abnormal laboratory findings in PGD for chromosomal abnormalities and aneuploidy screening. The poor representation of a 1- or 2-cell biopsy for the 7- or 6-cell post-biopsy embryo in the case of mosaicism explains the high rate of false-negative and false-positive results.

中文翻译：

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细胞遗传学正常，异常和镶嵌胚胎的发育：理论模型。

辅助生殖和植入前遗传学诊断（PGD）涉及各种复杂的技术，每种技术都有其自身的问题。但是，PGD对于染色体异常的最大问题不是技术性质，而是生物学现象：卵裂期胚胎中的染色体镶嵌。在这里，我们为染色体正常，异常和镶嵌胚胎的发育提供了一种假设的，定量的模型。通过二项式概率模型描述了在卵裂球中诱导染色体变化的有丝分裂事件的发生，从而描述了2-8细胞胚胎中镶嵌现象的产生。该模型将在横断面研究中发现的“平均”镶嵌率（60％）转换为到达8细胞阶段时相等的镶嵌胚率（59.8％）。>的消失 桑ula虫阶段有90％的镶嵌胚胎或存活的胚胎本身的镶嵌现象是通过在不断增强的细胞周期控制下大多数有丝分裂改变的细胞的有丝分裂停滞来解释的。在我们的模型中，在8细胞阶段的胚胎分别为正常和异常，分别为25.9％和14.3％。剩下的59.8％的胚胎显示出镶嵌性：34.6％的异常/正常细胞和25.2％的异常/异常细胞。高比例的异常和镶嵌胚胎共同解释了在PGD中用于染色体异常和非整倍性筛查的实验室异常发现的高发生率。在镶嵌术的情况下，对于7或6细胞活检后胚胎的1或2细胞活检的代表性较低，这说明假阴性和假阳性结果的发生率很高。