[Individual variability and inheritance of the number and size of the nucleolar organizer regions in chromosomes of domestic swine].

Individual variability of the number and size of silver-staining nucleolar organiser regions (NOR) was studied in 76 pigs of Semirechenskaya, Big White and Duroc breeds. The variability of the NOR number is exclusively caused by the presence of the 8NOR- allele (the chromosomes of the 8th homologous pair lacking the silver-staining NOR). Concentration of the 8NOR- allele is about 0.7 in the average for all three breeds. All 7 offsprings from the homozygous parents male 8NOR- /8NOR- and female 8NOR+/8NOR+ were heterozygotes 8NOR- /8NOR+. These data, together with good agreement between found and expected (according to the Hardy-Weinberg law) frequencies of homo- and heterozygotes suggest the codominant character of the NOR number inheritance. This allows using the NOR analysis to control the parentage announced. The study of inheritance of the size of NOR did not prove unequivocally its codominant character.