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2012.10.31:Rare floating chromosomal polymorphisms caused by translocation in frog Quasipaa boulengeri

 

 

    Very few natural polymorphisms involving interchromosomal reciprocal translocations are known in animal populations. The reasons are obvious because this kind of rearrangement can lead toreduction of fertility and reduced fitnessfor the carrier. Translocation heterozygotes will result in the formation of rings or chains of four chromosomes during meiosis and if they orientate with the adjacent centromeres passing to same poles (adjacent segregation) instead of to the opposite poles (alternate segregation), aneuploid gametes carrying either a duplication or a deficiency will be produced and would result inlower fecundity.

    In amphibians, there are no reports of fixed translocation polymorphisms in natural populations. So there's few information about the cytogenetic effect of translocation in amphibians even in vertebrates. Prof. ZENG Xiaomao, Dr. Qing Liyan and their colleagues from Chengdu Institute of Biology, Chinese Academy of Sciences examined 471 individuals from 33 populations using Giemsa stain or FISH or phylogenetic analysis and found that a mutual interchange occurred between chromosomes 1 and 6 and gave rise to rare translocation polymorphism.

    At least five different karyomorphs were observed in the pooled populations (Type I,MM/mm;II,MM/mSt;III,MT/mm;IV,MT/mSt;V,MT/StSt). Karyotype II, III and V were very rare in the populations. These results suggest that the translocation polymorphisms resulted from the union of gametes produced by alternate and adjacent-1 meiotic segregation modesbut not by adjacent-2 segregation.

    The mutual translocation likely evolved just once in this species and the dispersal of the one karyomorph (type IV) can explain the chromosomal variations among populations. The phylogenetic inference proved that all populations of Q. boulengeri grouped into a monophyletic clade and suggested that the populations possessing translocated karyomorphs and those without any heteromorphic karyotypes did not diverge significantly from each other.

    This study entitled "A de novo case of floating chromosomal polymorphisms by translocation in Quasipaa boulengeri (Anura, Dicroglossidae)" was published in PLOS ONE on October 3rd, 2012. You can find the complete article at http://dx.plos.org/10.1371/journal.pone.0046163.