In humans, one of the 2 alleles of ACE has 287 more base pairs in its DNA and is called the long allele; whereas the other is the short allele. All humans have 2 ACE genes. Roughly, 50 % of humans have one copy of each variant, 25 % have 2 short genes and 25 % have the 2 long ones, depending on race or national population. What really prevails in horses, and the various effects on SPEED are unknown.