Day 12 CFU-S are not significantly reduced in HOXA9−/− mice. In experiments using pooled marrow samples, marrows from 2 to 3 HOXA9−/− mice were pooled and compared with pooled marrows from 2 to 3 HOXA9+/+ mice. Recipient animals (3 to 4 mice per dose of cells) were injected with either 50,000 or 100,000 pooled cells. In the experiment using individual samples, single marrow samples from 3 homozygous and 3 C57 animals were injected into cohorts of lethally irradiated C57 animals, using the same doses of cells. In 2 of 3 experiments, there was a minor and statistically insignificant reduction in the frequency of day 12 CFU-S in HOXA9−/− mice.