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a, PowerPlex16 STR genotyping of DNA from matched maternal and fetal samples (decidua, maternal blood and placenta) to identify origin of organoids. The 15 STR loci analysed are shown. Numbered STR alleles observed for each DNA at a particular locus are listed within the relevant column. As expected, in most cases a maximum of two alleles was seen, but where there was lesser evidence of an additional allele from a fetal derived STR haplotype the allele number appears in brackets. The results at informative loci in which maternal blood, decidua and decidual organoids match are underlined. b, HLA genotyping with LABType reverse sequence-specific oligonucleotide probes (SSOP) of DNA from four pregnancies with matched decidua, blood, placenta and organoids. Each pair of HLA alleles defined, at low resolution, for each sample at a particular locus is listed within the relevant column. The maternal origin of the organoids is clear from HLA-A, HLA-B and HLA-C alleles in three of the four pregnancies. The data were inconclusive for pregnancy two, but all four organoids are clearly maternal in origin when using both methods (see above).