Fig. 2. The effect of Pafr expression and embryo density on the development of zygotes in vitro. Pafr+/+ or Pafr–/– embryos were cultured either individually (1/10) or in groups of 10 (10/10) in 10 µl drops of media for 96 hours. (A) The proportion of embryos achieving expected developmental landmarks at each 24 hour interval was assessed, and (B) for those zygotes that developed to morphologically normal blastocysts after 96 hours culture the number of cells per embryo (mean ± s.d.) with apparently normal or obviously fragmented nuclei was assessed.