Sharbel T F, Green D M, Houben A
Redpath Museum, McGill University, Montréal QC, Canada.
Genome. 1998 Feb;41(1):14-22. doi: 10.1139/gen-41-1-14.
The endemic New Zealand frog Leiopelma hochstetteri has variable numbers of mitotically stable B chromosomes. To assess whether the B chromosomes were derived from the autosome complement, they were isolated by micromanipulation and their DNA amplified by degenerate oligonucleotide primed PCR. Southern hybridizations of B chromosome DNA probes to genomic DNA from males and females characterized by differing numbers of B chromosomes demonstrated that the B chromosomes were derived from the univalent W sex chromosome characteristic of North Island populations. The presence of homologous B chromosome specific sequences from geographically distinct populations indicates a single origin of the B chromosomes. Furthermore, a primitive homology shared by B chromosomes and the W sex chromosome from an ancestral WZ/ZZ karyotype, which is still present in frogs from Great Barrier Island, shows that the B chromosomes originated soon after the univalent W sex chromosome had originated. Sequence analysis revealed that B chromosome DNA is composed of repeat sequences and has the potential to form stable hairpin structures. The molecular dynamics of these structures may reflect an inherent propensity to undergo rapid change in nucleotide sequence and chromosome structure.
新西兰本土蛙类霍氏滑跖蟾（Leiopelma hochstetteri）具有数量可变的有丝分裂稳定B染色体。为了评估B染色体是否源自常染色体组，通过显微操作将它们分离出来，并使用简并寡核苷酸引物PCR扩增其DNA。用B染色体DNA探针与具有不同数量B染色体的雄性和雌性基因组DNA进行Southern杂交，结果表明B染色体源自北岛种群特有的单价W性染色体。来自地理上不同种群的同源B染色体特异性序列的存在表明B染色体有单一的起源。此外，B染色体与来自祖先WZ/ZZ核型的W性染色体共有的原始同源性（大堡礁岛的蛙类中仍然存在这种核型）表明，B染色体在单价W性染色体起源后不久就出现了。序列分析表明，B染色体DNA由重复序列组成，并且有形成稳定发夹结构的潜力。这些结构的分子动力学可能反映了核苷酸序列和染色体结构快速变化的内在倾向。
