Fig. 4

Formation mechanisms of mosaic aneuploidy and UPD in four cases. A In case 1, the maternal chr2 was crossed over in meiosis I prophase, and then, multiple adverse events, such as non-separation of the second meiosis, trisomy rescue, and monomeric self-rescue, occurred continuously on chr2 during meiosis and mitosis Chr2 consisted of normal cell, trisomy, and matUPD disomy cells. B In case 2, the maternal chr15 were homologous recombination in meiosis I prophase, then, non-separation of the meiosis II, trisomy rescue of the trisomic zygote happened on chr15 during meiosis and mitosis. Chr15 consisted of normal cells, trisomy, and matUPD disomy cells. C Three adverse events occurred successively in case 3, including endoreduplication and monomer rescue of the paternal genome and loss of a chrX in some cells during the anaphase of mitosis. Thus, a mosaic consisted of paternal whole genome UPD, biparental 46,XX, and 45,X cells. D For case 4, two adverse events occurred in succession, including no separation in the MII phase of the ovum and trisomy self-rescue of chr20. However, very few trisomy cells remained after an incomplete self-rescue. Thus, the mosaic compositions in uncultured amniocytes were maternal UPD(20) cells (> 90%) and T20 cells (< 10%), estimated by the detection limit of the CMA and CNV-seq