Nineteen metaphase cells stained for the structural heterochromatin (C-banding) were analyzed. The clearly stained pericentromeric heterochromatic blocks, which sizes were approximately the same, were identified at all chromosomes of Ochotona huangensis. The heteromorphism was detected by localization of heterochromatic blocks on the 8-th pair of autosomes. An intercalary heterochromatic block was always detected in the long arm of one homologue of the 8-th pair. Also, that homologue had the pericentromeric block of heterochromatin. In the second homologue of this pair, the intercalary heterochromatic block was detected in nine metaphase cells. In the remaining cells, only the larger pericentromeric heterochromatic block was detected in this homologue. By that, the euchromatic site, which separates the intercalary heterochromatic block, was broader on the first homologue than that on the second homologue (Fig. 4). We can’t characterize this phenomenon in details and discuss about its nature, because of the absence of sufficient material. So we leave it only as an observed fact. The X chromosome has a pericentromeric block of heterochromatin. The heterochromatic region occupies 2/3 of the lower arm on the Y chromosome (Fig. 3a).
The Daurian pika, which like Ochotona huangensis belongs to the subgenus Ochotona, was studied for a comparative karyotype analysis. The karyotype of Ochotona dauurica contains 50 chromosomes (NFa=68) which are grouped in 10 meta-submetacentric pairs (3 large, 2 medium and 5 small) and 14 subtelo- and acrocentric pairs of autosomes. The X chromosome is a submetacentric, similar in size to the 3-rd or 4-th pairs of autosomes, the Y chromosome is a very small acrocentric (Fig. 2b). The karyotype of the Daurian pika does not differ from that which was previously described in the literature (Vorontsov and Ivanitskaya 1969, 1973).
Analysis of 15 C-stained metaphase plates showed that all autosomes of Ochotona dauurica have the large pericentromeric heterochromatic blocks which were intensively stained. The 10-th and 15-th – 22-th pairs of autosomes have completely heterochromatic short arms. The last two small pairs of autosomes (23-th and 24-th) are composed of heterochromatin entirely. The large pericentromeric block of the X chromosome occupies 1/3 of the long arm. Heterochromatic structure of the Y chromosome was not confirmed (Fig. 3b) compared with published data (Ivanitskaya 1991).