Checking the genotype of all the blastomeres in the repaired embryos, we found that most of them were mosaic, containing homozygous mutant blastomeres and repaired blastomeres (Table 1). Of the 7 repaired embryos with more than 2 successfully sequenced blastomeres, the percentage of repaired blastomere was between 20% and 75% (Table 1). In addition, the sequenced blastomere from embryo #14, with 1 successfully sequenced blastomeres, was wild-type (1/1, 100%). The high percentage of repaired blastomere suggests the possibility of getting repaired embryos free of mosaicism. These data demonstrate that it is feasible to correct HBB −28 (A>G) mutation in human embryos efficiently and specifically by base editor.