Figure 1.

Diploid uniparental embryos and overgrowth phenotype of AG ES cell chimeras. (A) Activation of an unfertilized oocyte and suppression of second polar body extrusion results in a diploid parthenogenetic embryo. GG and AG embryos with two maternal or paternal genomes from two oocytes or sperm, respectively, can be produced experimentally by pronuclear transfer between zygotes.⁹⁸ Alternatively, AG embryos can be produced by in vitro fertilization⁹⁹ or, presumably, by intracytoplasmic sperm injection of enucleated donor oocytes, procedures not involving fertilized embryos. (B) Overgrowth phenotype of an AG ES cell chimera (right) at E 16.5 compared to normal littermate (left). Contribution of AG cells visualized by EGFP fluorescence in E 16.5 AG chimera (AG ES cells are EGFP transgenic).