MSTN and osteopetrosis: The aim of the study was the screening of the Russian populations of Aberdeen Angus, Hereford and Belgian Blue cattle on gene mutations associated with the genetic defects of arthrogryposis multiplex (AM), osteopetrosis (OS), developmental duplication (DD), double muscling (M1), hypotrichosis (HY) and maple syrup urine disease (MSUD) as well as the <i>F94L</i> polymorphism of myostatin gene (<i>MSTN</i>) linked with the gene responsible for less fat content in the carcass by means of DNA analysis.