Toder R, O'Neill R J, Wienberg J, O'Brien P C, Voullaire L, Marshall-Graves J A
School of Genetics and Human Variation, La Trobe University, Kingsbury Drive, Bundoora, Victoria 3083, Melbourne, Australia.
Mamm Genome. 1997 Jun;8(6):418-22. doi: 10.1007/s003359900459.
Cross-species chromosome painting was used to investigate genome rearrangements between tammar wallaby Macropus eugenii (2n = 16) and the swamp wallaby Wallabia bicolor (2n = 10female symbol/11male symbol), which diverged about 6 million years ago. The swamp wallaby has an XX female:XY1Y2 male sex chromosome system thought to have resulted from a fusion between an autosome and the small original X, not involving the Y. Thus, the small Y1 should represent the original Y and the large Y2 the original autosome. DNA paints were prepared from flow-sorted and microdissected chromosomes from the tammar wallaby. Painting swamp wallaby spreads with each tammar chromosome-specific probe gave extremely strong and clear signals in single-, two-, and three-color FISH. These showed that two tammar wallaby autosomes are represented unchanged in the swamp wallaby, two are represented by different centric fusions, and one by a tandem fusion to make the very long arms of swamp wallaby Chromosome (Chr) 1. The large swamp wallaby X comprises the tammar X as its short arm, and a tandemly fused 7 and 2 as the long arm. The acrocentric swamp wallaby Y2 is a 2/7 fusion, homologous with the long arm of the X. The small swamp wallaby Y1 is confirmed as the original Y by its painting with the tammar Y. However, the presence of sequences shared between the microdissected tammar Xp and Y on the swamp wallaby Y2 implies that the formation of the compound sex chromosomes involved addition of autosome(s) to both the original X and Y. We propose that this involved fusion with an ancient pseudoautosomal region followed by fission proximal to this shared region.
跨物种染色体涂染技术被用于研究帚尾袋鼩（Macropus eugenii，2n = 16）和沼袋鼩（Wallabia bicolor，2n = 10♀/11♂）之间的基因组重排，这两个物种大约在600万年前分化。沼袋鼩具有XX雌性：XY1Y2雄性性染色体系统，据认为这是由一条常染色体与原始小X染色体融合形成的，不涉及Y染色体。因此，小的Y1应该代表原始的Y染色体，而大的Y2代表原始的常染色体。从帚尾袋鼩经流式细胞分选和显微切割的染色体中制备了DNA涂染探针。用每种帚尾袋鼩染色体特异性探针涂染沼袋鼩的染色体涂片，在单色、双色和三色荧光原位杂交中都给出了极其强烈和清晰的信号。这些结果表明，帚尾袋鼩的两条常染色体在沼袋鼩中未发生变化，两条由不同的着丝粒融合所代表，一条由串联融合形成沼袋鼩染色体（Chr）1的非常长的臂。沼袋鼩的大X染色体以帚尾袋鼩的X染色体作为短臂，以及串联融合的7号和2号染色体作为长臂。近端着丝粒的沼袋鼩Y2是2/7融合体，与X染色体的长臂同源。小的沼袋鼩Y1通过与帚尾袋鼩Y染色体的涂染被确认为原始的Y染色体。然而，在显微切割的帚尾袋鼩Xp和Y染色体上共有的序列出现在沼袋鼩Y2上，这意味着复合性染色体的形成涉及向原始的X和Y染色体都添加了常染色体。我们提出，这涉及与一个古老的拟常染色体区域融合，随后在这个共享区域近端发生裂变。
