Homeobox protein Hox-A9 is a protein that in humans is encoded by the HOXA9 gene. In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four separate chromosomes. Expression of these proteins is spatially and temporally regulated during embryonic development. This gene is part of the A cluster on chromosome 7 and encodes a DNA-binding transcription factor which may regulate gene expression, morphogenesis, and differentiation. This gene is highly similar to the abdominal-B (Abd-B) gene of Drosophila fly. A specific translocation event which causes a fusion between this gene and the NUP98 gene has been associated with myeloid leukemogenesis. As HOXA9 dysfunction has been implicated in acute myeloid leukemia, and expression of the gene has been shown to differ markedly between erythrocyte lineages of different stages of development, the gene is of particular interest from a hematopoietic perspective.