Svartman Marta, Stone Gary, Page John E, Stanyon Roscoe
Comparative Molecular Cytogenetics Core, Genetics Branch, National Cancer Institute-Frederick, Frederick, MD 21702, USA.
Chromosome Res. 2004;12(1):45-53. doi: 10.1023/b:chro.0000009294.18760.e4.
We studied the chromosomes of an Afrotherian species, the short-eared elephant shrew Macroscelides proboscideus with traditional banding techniques and mapped the homology to human chromosomes by in-situ hybridization of human chromosome paints. Here we present for the first time the karyotype of this species, including banding patterns. The chromosome painting allowed us to test various hypotheses of the ancestral Eutherian karyotype, the validity of the radical taxonomic assemblage known as Afrotheria and the phylogenetic position of the elephant shrew within the Afrotheria. Current hypotheses concerning the Eutherian ancestral karyotype include diploid numbers ranging from 2n = 44 to 50 while molecular studies have proposed a new superordinal grouping of extant Eutherians. In particular, the Afrotheria is hotly debated, as it appears to be an odd mixture of species from Ungulata, Tubulidentata, Macroscelidea and Lipotyphla, which have no apparent morphological traits to unite them. The hybridization pattern delimited a total of 37 segments in the elephant shrew genome and revealed 21 different associations of human chromosome segments. Associations 1/19 and 5/21 link all Afrotheria so far studied and support the Afrotheria assemblage. Associations 2/8, 3/20, and 10/17 strongly link aardvarks and elephant shrews after the divergence of the line leading to elephants. The most likely ancestral Eutherian karyotype would be 2n = 48 chromosomes. However, the lack of comparative chromosome painting data between Eutherians and an appropriate outgroup is a severe limitation on attempts to delineate the ancestral genome of Eutherians. Current attempts lack legitimacy until this situation is corrected.
我们使用传统的染色体显带技术研究了非洲兽总目的一个物种——短耳象鼩（Macroscelides proboscideus）的染色体，并通过人类染色体涂染原位杂交技术将其与人类染色体的同源性进行了定位。在此，我们首次展示了该物种的核型，包括染色体带型。染色体涂染使我们能够检验有关真兽类祖先核型的各种假说、被称为非洲兽总目的激进分类组合的有效性以及象鼩在非洲兽总目内的系统发育位置。目前关于真兽类祖先核型的假说包括二倍体数从2n = 44到50不等，而分子研究提出了现存真兽类的一个新的超目分类。特别是，非洲兽总目备受争议，因为它似乎是有蹄类、管齿目、象鼩目和食虫目物种的奇特混合，这些物种没有明显的形态特征将它们统一起来。杂交模式在象鼩基因组中划定了总共37个区段，并揭示了人类染色体区段的21种不同组合。组合1/19和5/21将迄今为止研究的所有非洲兽总目动物联系起来，支持了非洲兽总目的分类组合。组合2/8、3/20和10/17在导致大象的谱系分化后，将土豚和象鼩紧密联系起来。最可能的真兽类祖先核型可能是2n = 48条染色体。然而，真兽类与合适的外类群之间缺乏比较染色体涂染数据，这严重限制了描绘真兽类祖先基因组的尝试。在这种情况得到纠正之前，目前的尝试缺乏合理性。
