Genotyping the progeny of miR-142 +/− intercrosses at embryonic day 14.5 (E14.5) revealed the predicted Mendelian distribution of miR-142 +/+ , miR-142 +/− , and miR-142 −/− embryos. However, postnatal survival at 3 weeks of age of miR-142 homozygous offsprings was lower than expected (18% instead of 25%), demonstrating that roughly a third of miR-142 −/− mice died perinatally (Figure 1-source **data** 1). Surviving miR-142 −/− mice did not display overt physical abnormalities, were fertile, and bred normally.