Homologous fission event(s) implicated for chromosomal polymorphisms among five species in the genus <i>Equus</i>

Abstract

The genus Equus is unusual in that five of the ten extant species have documented centric fission (Robertsonian translocation) polymorphisms within their populations, namely E. hemionus onager, E. hemionus kulan, E. kiang, E. africanus somaliensis, and E. quagga burchelli. Here we report evidence that the polymorphism involves the same homologous chromosome segments in each species, and that these chromosome segments have homology to human chromosome 4 (HSA4). Bacterial artificial chromosome clones containing equine genes SMARCA5 (ECA2q21 homologue to HSA4q31. 21) and UCHL1 (ECA3q22 homologue to HSA4p13) were mapped to a single metacentric chromosome and two unpaired acrocentrics by FISH mapping for individuals possessing odd numbers of chromosomes. These data suggest that the polymorphism is either ancient and conserved within the genus or has occurred recently and independently within each species. Since these species are separated by 1–3 million years of evolution, this polymorphism is remarkable and worthy of further investigations.

Multidirectional cross-species painting illuminates the history of karyotypic evolution in Perissodactyla

“…If this is true, it may have been fixed, fused with other chromosomes, or independently disrupted in various lineages. This hypothesis is supported by the occurrence of an ECA 2q/3q polymorphism that was detected in extant populations of onager, kulan, kiang, Somali wild ass, and Burchell_s zebra (Myka et al 2003). Alternatively, this synteny could be susceptible to fission (Myka et al 2003), leading to convergence in various lineages through reuse of this particular breakpoint.…”

“…The ambiguity in the diploid number may be explained by the potentially ancestral polymorphic state of some perissodactyl chromosomes (e.g. ECA 2q/3q, Myka et al 2003) or, alternatively, breakpoint reuse and convergent fusion/fission events.…”

A Rare Case of Centric Fission and Fusion in a River Buffalo (Bubalus bubalis, 2n = 50) Cow with Reduced Fertility

“…It has been rarely reported in humans [Sinha et al, 1972;Bogart et al, 1995;Bakshi et al, 2003;Perry et al, 2004;Shim et al, 2007]. In domestic animals centric fissions have been found only in donkey [TrommershausenBowling and Millon, 1988;Houck et al, 1998;Myka et al, 2003;Alaoui et al, 2004]. In the present study centric fission of BBU1 was followed by centric fusion of BBU1p with BBU23, probably after a reciprocal translocation between BBU1 and BBU23.…”

Chromosome Evolution in Perissodactyla

“…It is conserved in Malayan tapir, zebras, kulan and donkey, but disrupted at the same position in all other tapirs, rhinoceroses, onager, kiang and horse. Actually, chromosome painting was only done on a few individuals and it is necessary to add that there is a Robertsonian polymorphism of PAK1 detected in extant populations of Asiatic asses, Somali wild ass and Burchell's zebra [Myka et al, 2003]. We believe that the current situation represents a typical example of hemiplasy or ancient polymorphism, where the same elements were fixed in fused or disrupted state in different species.…”