Parental genomes segregate into different blastomeres during multipolar zygotic divisions leading to mixoploid and chimeric blastocysts
The zygotic division enables two haploid genomes to segregate into two biparental diploid blastomeres. This fundamental tenet was challenged by the observation that blastomeres with different genome ploidy or parental genotypes can coexist within individual embryos. We hypothesized that whole parental genomes can segregate into distinct blastomere lineages during the first division through "heterogoneic division". Here, we map the genomic landscape of 82 blastomeres from 25 embryos that underwent multipolar zygotic division. The coexistence of androgenetic and diploid or polyploid blastomeres with or without anuclear blastomeres, and androgenetic and gynogenetic blastomeres within the same embryo proofs the existence of heterogoneic division. We deduced distinct segregation mechanisms and demonstrate these genome-wide segregation errors to persist to the blastocyst stage in both human and cattle. Genome-wide zygotic segregation errors contribute to the high incidence of embryonic arrest and provide an overarching paradigm for the development of mixoploid and chimeric individuals and moles.