Cytogenetic and molecular studies of different species of raccoon dog (Nyctereutes procyonoides)

The raccoon dog (Nyctereutes procyonoides) is recognized as the oldest representative of the family Canidae and represents a distinct branch on the phylogenetic tree. The raccoon dog karyotype contains many segments homologous to chromosomes from the predicted ancestral karyotype for the order. Carnivora were identified. Thus, it was suggested that the raccoon dog has the most primitive karyotype in the family Canidae. Two subspecies are recognized: the Chinese raccoon dog Nyctereutes procyonoi-des procyonoides (N.p.p.) and the Japanese raccoon dog Nyctereutes procyono-des viverrinus (N.p.v.). The karyotype of the Chinese raccoon dog (2n = 54 + B) consists of five pairs of biarmed autosomes and 21 pairs of acrocentric autosomes. The sex chromosomes are also biarmed, with the medium-sized X and Y chromosome being the smallest chromosome in the karyotype. In addition, there is a variable (1–4) number of B chromosomes in this karyotype. A proposal for chromosome nomenclature for the Chinese raccoon dog was recently presented. The karyotype of the Japanese raccoon dog (2n = 38 + B) includes 13 pairs of biarmed chromosomes, 5 pairs of acrocentric chromosomes, and biarmed X and Y chromosomes. This subspecies also has a variable number (2–7) of B chromosomes. Although the karyotypes of both subspecies differ in chromosome number and morphology, they have the same fundamental number of chromosome arms – 66. The raccoon dog has fairly large acrocentric B chromosomes. They differ in size in the two subspecies. In the Chinese raccoon dog, these are medium-sized acrocentrics, while in the Japanese raccoon dog, they are small acrocentrics. Bs are rather positive for C banding; however, the patterns of Cb banding are not as distinct as in autosomal centromeres. R banding has shown that these structures are late replicators.