2009/02/12 by Úlfur Árnason · 1 voice
Agricultural and Biological Sciences · Biochemistry, Genetics and Molecular Biology · Environmental Science · #Chromosomal and Genetic Variations #Genomics and Phylogenetic Studies #Ichthyology and Marine Biology
paper · doi:10.1111/j.1601-5223.1981.tb01727.x
A silver-staining technique was used for determining the localization of nucleolar organizing regions (NORs) in the four principal pinniped karyotypes. The otariid and odobenid karyotypes were represented by Arctocephalus pusillus (2n=36) and Odobenus rosmarus (2n=32), respectively. The 2n=34 phocid karyotype was represented by Cystophora cristata and the 2n=32 karyotype by Phoca largha and P. fasciata. In each of the karyotypes, only one pair carries a NOR site. This is consistent with the presence of a secondary constriction in one pair only. The limited differences that separate the otariid and odobenid karyotypes involve the NOR pair. The otariid NOR pair is a rather small metacentric with the NOR site in the shorter arm. The odobenid NOR pair is a rather large submetacentric with the NOR site in the middle of the long arm. The translocation separating the 2n=34 and 2n=32 phocid karyotypes also involves the NOR pair. Thus, the chromosomal localization of NOR is not rigid. Together with recent advances in pinniped paleontology, the present results were interpreted as consistent with diphyletic origin of the pinnipeds from two ancestral lineages, one otariid—odobenid and one phocid, which entered the marine environment separately.