Investigation On The Formation And Genetic Traits Of Hybrids Derived From Female Koi Carp(Cyprinus Carpio Haematopterus,♀)× Male Rare Minnow(Gobiocypris Rarus,♂)

Various fish strains obtained through distant hybridization may have important values in genetic breeding and biological evolution.In this study,the koi carp（Cyprinus carpio haematopterus,KOC,2n=100,♀）in the subfamily of cyprinus and the rare minnow（Gobiocypris rarus,GR,2n=50,♂）in the subfamily of cyprinidae is used for distant hybridization to obtain diploid hybrid carp and triploid hybrid carp.The main research contents of this article include:1.The appearance characteristics,DNA content,chromosome number,red blood cell morphological characteristics and gonadal development of the two ploidy hybrid carp in the KOC,GR and F₁ generation were compared and analyzed.The results of flow cytometry and chromosome sections showed that the number of chromosomes of hybrid carp was 75and 125,which indicated that the progeny of the two species were heterodiploid and heterotriploid,respectively.The main measurable traits（caudal stalk length/caudal stalk height,head length/head height,body length/body height）and the conuted traits（numbers of fin,lateral line scale,lateral line upper scale,lateral line lower scale）of the heterodiploid carp were more close to the paternal parent,the phenotypic characteristics of allotriploids are closer to those of the female parent.The nucleus size of red blood cells in KOC,GR and F₁ generation was positively correlated with the DNA content contained in it,and the red blood cells of the triploid carp showed nuclear division,while no division of blood cells is observed in the diploid carp.The development results of gonad showed that the gonad development of the two different ploidy hybrids were lagging,and the tissue sections showed that a certain proportion of shrunken cells appeared in the gonads of the hybrids,suggesting the existence of apoptosis.2.The mitochondrial genes（12S r RNA,16Sr RNA,ND1,ND2,ATPase,ND4,ND56,Cytb and CR）of KOC,GR,and two ploidy F₁ hybrid carp was partially amplified by PCR,and the structural variation of mitochondrial sequence was analyzed.The results showed that the mitochondrial sequences of the two hybrid carp were basically consistent with the female parent’mitochondrial sequences and indicated mitochondrial inheritance following the rules of maternal inheritance.3.It was found that the mosaic phenomenon existed in both 5S r DNA and Hox A4a,Hox A2b,Hox B5b,Hox C4a and Hox D10a of the two ploidy F₁ hybrid carp,indicating that the distance hybridization caused the variation of the genomic DNA level of the two hybrid fish.4.The expression bias and relative expression levels of four growth-related genes（pik3r1,gh,igf,mstn）of two different ploidy hybrid carp in the parent and F1 generation were analyzed.By analyzing the expression bias of the parents and the two ploidy hybrid carp,the results showed that the pik3r1,igf and mstn of the two hybrid offspring and the CDS sequence of the gh gene of the triploid carp were mainly the same as the female parent.Its expression is biased towards the female parent,and the CDS sequence of the diploid carp gh gene is mainly the same as the male parent,indicating that its expression is biased towards the male parent.The expression levels of pik3r1,igf,mstn in both hybrid progeny and gh the hybrid triploid are between the parent,while gh gene expression of the diploid hybrid is significantly lower than that of the parental and triploid hybrid fish.Among them,the expression levels of the gh and igf,which supposed to be promoting growth in the triploid progeny are higher than those in the diploid progeny,while the expression levels of pik3r1 and mstn,supposed inhibiting growth,in the triploid progeny are lower than those in the diploid progeny.Regarding the expression levels in the diploid progeny,the expression patterns of these four genes are consistent with the phenomenon that the growth of triploid common carp is significantly faster than that of diploid carp.In this study,the heterodiploid hybrid carp and allogeneic triploid hybrid carp were successfully obtained through of distant hybridization.The two hybrid fishes are exhibited variability and heritability at the appearance characteristics and the molecular level such as Hox gene,5S r DNA,and mitochondrial genome.