A comparison of high-altitude and low-altitude Ethiopian cattle breeds showed high genetic differentiation between the populations for multiple genes associated with hypoxia, including BDNF (brain-derived neurotrophic factor), TFRC (transferrin receptor) and PML (promyelocytic leukemia), suggesting that these genes have been selected for increased hypoxia tolerance [56]. This evidence concerns the gene BDNF and acute promyelocytic leukemia.