Although we would have expected that in apoptotic cells, the pro-apoptotic genes would be upregulated, the downregulation of all the genes contradicts the known mechanisms initiated by apoptotic cells; that means this unknown mechanism changes the ratio in favor of the pro-apoptotic vs. the anti-apoptotic genes. It appears speculative that apoptosis was prevented to some extent when eggs were incubated (incubation involves application of heat and O2 to eggs to initiate embryo development), as indicated by the gene expression results at the embryonic d-6 level; however, previous studies have shown that warming eggs before incubation appears to improve embryo quality, increase the number of viable embryonic cells, and improve hatchability, which may have been due to the restricted expression of the pro-apoptotic genes (Fasenko et al., 2001; Reijrink et al., 2010).