| The improved diploid mirror carp species（IDMC-F1,2n=100）（17.5%）are one of the four different ploidy fertile types,derived from the distant hybridization of common carp（Cyprinus carpio L.,COC,2n=100）（♀）×blunt snout bream（Megalobrama amblycephala,BSB,2n=48）（♂）.We obtained the hybrid lineage（IDMC-F1-F2）from the self-breeding of IDMC-F1.The study aims to research the genetic characteristics of IDMC-F1-F2,including the structural composition and genetic variation of 5S rDNA and Hox genes in genomic DNA.The details are as follows:（1）In terms of characteristics of appearance,we found that there were significant differences between IDMC-F1,IDMC-F2 and their parents in morphological characteristics,such as less scales throughout the body;body shape is relatively flat and stout;body color is light yellow and tail color is not obviously red.（2）In the aspect of genetic characteristics of 5S rDNA,it revealed that part of the 5S rDNA fragments of IDMC-F1 and IDMC-F2 inherited5S rDNA fragments of COC,some of the 5S rDNA fragments had some degrees of variation due to substitution,deletion or insertion of base in NTS region and the others were composed of different 5S rDNA fragments.Compared with IDMC-F1,IDMC-F2 had more obvious recombination events.（3）In genetic characteristics of Hox genes respect,it showed that Hox genes of IDMC-F1 and IDMC-F2 had undergone some degrees of variation and the Hox gene recombination clusters derived from IDMC-F1 and IDMC-F2.We also found pseudogenes in the recombinant clusters.But almost all of Hox gene clusters in IDMC-F1 were inherited by IDMC-F2,but IDMC-F2 contained more recombination events,including chimerism of the male parent（BSB）Hox gene fragments and the female parent（COC）Hox gene fragments.The results of the phylogenetic tree constructed from twelve Hox genes showed that IDMC-F1 and IDMC-F2 had a close relationship with BSB due to the embedding of the genetic material of BSB.The structural composition and genetic variation of the Hox genes also proved that the Hox gene clusters are undergoing continuous degeneration in the cyprinid fishes,with some genes gradually becoming pseudogenes,and some genes completely pseudogenised.It revealed that genomic DNA of IDMC-F1 and IDMC-F2 not only inherited genomic DNA of COC,but also embedded some DNA fragments of BSB at molecular biology level.The origin and morphological characteristics of IDMC-F1 and IDMC-F2 provided important evidence for speculation that mirror carp may be formed through common carp（♀）×blunt snout bream（♂）in nature. |
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