FIG. 5.

sir2α null animals are not lost during fetal development but are smaller and occasionally have exencephaly. Animals heterozygous for the mutant sir2α allele were mated, and fetuses were harvested at daily intervals after embryonic day 9.5. The fetal membranes were used to isolate DNA for genotyping, and the corresponding embryo was fixed. The genotypes were present in the expected ratios, and there was no evident downward trend in the proportion of the sir2α null genotype. The sir2α null embryos were usually smaller than their littermates. This size difference was evident as early as embryonic day 12.5. Two of the sir2α null embryos had exencephaly, as indicated with the arrow in panel B. Bars, 0.5 cm.