Mitochondrial DNA of the pigeons is already sequenced ("Characterization of the complete mitochondrial genome of the Rock pigeon, Columba livia (Columbiformes: Columbidae)", X.Z. Kan, X.F. Li, L.Q. Zhang, L. Chen, C.J. Qian, X.W. Zhang and L. Wang 2010) These scientists found only 35 genes coded in the mtDNA versus approx. 20.000 genes in the rest of the DNA (like I said already above). Until today there was only one polymorphism found on one of these 35 genes. And only this can can generate different phenotypes (different properties in the birds). It is the MTCYB (Cytochrom B) gene. And this gene in fact is active in a subunit, responsible for cell metabolism and so for the performance of the cell (look here: "A new PCR-RFLP within the domestic pigeon (Columba livia var. domestica) cytochrome b (MTCYB) gene", Andrzej Dybus, Kamila Knapik, 2005). But like i also said already above, they only found one version of this gene (allele) in all racing pigeons. In other kinds of pigeons like Strasser, Highflyer or Carrier the found also the other version. So if the second version found in Highflyers is not as good as the other, then the the selection of racing pigeons over a period of 200 years has already eliminated the suboptimal version in all racing pigeons today.