Study On Genetic And Reproduction Characteristics Of The Offspring Of The Hybrids Between Koi Carp And Blunt Snout Bream

Distant hybridization refers to the hybridization between species,genera,or even distantly related species.Distant hybridization is an important way to form new species.Bisexual and fertile Red crucian carp-like fish(RCC-L,2n=100)and Gynogenetic koi carp(GKOC,2n=100)were cultivated through distant hybridization of Cyprinus carpio haematopterus(KOC,2n = 100,♀)and Megalobrama amblycephala(BSB,2n = 48,♂).By self-cross RCC-L can generate 98%RCC-L and 2%GF-L.The main contents of this paper include:Firstly,the results of studies on the appearance characteristics of RCC-L,KOC and GF-L contains two aspects.On the one hand,RCC-L resembled RCC in shape(eg,body size,body color),and there are significant differences between the female parent and the male parent.On the other hand,RCC-L has a white background,red and yellow patterns,bright black eyes,transparent body,is a good material for studying genetic variation.In appearance,GKOC has a high degree of consistency with the KOC.GF-L resembles ordinary goldfish in shape,with a short tail stem and high body back.Secondly,the ploidy levels and chromosome composition of the two hybrids and their parents,KOC and BSB were analyzed by flow cytometry,caudate fin culture technique,chromosome counting and karyotype.In the progenies of KOC and BSB,all the chromosome number of RCC-L,GF-L and GKOC is 100,which is consistent with the chromosome number of KOC.The DNA content was not significantly different from that of KOC(P>0.05).There was a significant difference(P<0.05)between the BSB and the KOC in DNA content,and the karyotype formula was 22m+34sm+22st+22t.Thirdly,observation of the gonads of RCC-L,GKOC and GF-L through Paraffin section,shows that RCC-L and GF-L maturation at one year old,but GKOC maturation at two years old.Observing the semen of RCC-L and GF-L with scanning electronic microscope,we found that both of their sperms has normal-sized head and normal-swimming tail.The amino acid content of muscle in RCC-L,and its parents(KOC and BSB)was determined by amino acid analyzer.The results showed that the amino acid content of the RCC-L was higher than that of the parents(KOC and BSB),which can provide parental sources for other combinations of distant hybridization,such as White crucian carp X red crucian carp and Triploid crucian carp.Fourthly,the genome of KOC,BSB and RCC-L was tested using restriction endonuclease polymorphism(AFLP).The results showed that the genetic distance of RCC-L to BSB was greater than the genetic distance of RCC-L to KOC.Microsatellite analysis(SSR)revealed that the heterozygous and polymorphic information content of RCC-L was higher than that of RCC,showing that RCC-L genome is in the concussion phase.Fifth,in this study,5S rDNA(340 bp,GQ485556)and crucian carp-specific repetitive sequence(263bp,JQ086761)were used as probes for chromosome.5S rDNA 340 bp(FISH)analysis of KOC,BSB,RCC-L,RCC showed two strong signals and two weak signals were both found in RCC-L and RCC.The crucian carp-specific repetitive sequence can find signals on 100 chromosomes of RCC.Likewise,100 signals can be found on chromosomes of RCC-L.Both probes can not find signals on chromosomes of KOC and BSB.Sixth,analysis of the mitochondrial genome sequence of KOC,BSB,RCC-L,GF-L showed that the similarities of mitochondrial sequence between RCC-L and RCC(98.4%)was higher than that between RCC-L and KOC(89.3%)and between RCC-L and BSB(75.9%).In terms of variability,the variation rate of RCC-L and RCC was 1.30%,the variation rate of RCC-L and BSB was 16.40%,the variation rate of RCC-L and KOC was 11.10%.The similarities and variability comparisons showed that RCC-L mitochondria had the highest homology with the RCC mitochondrial sequences,which due to the insertion of the gene fragment of BSB lead to the mitochondrial structure of RCC-L was changed,and its mitochondrial structure tended to be the mitochondrial structure of crucian carp.Seventh,studies on the structure of 5S rDNA,Hox genes and Sox genes in the genomic DNA of the KOC,BSB,RCC-L and GF-L,we found RCC-L and GF-L are derived from the 5S rDNA of the KOC,and the Hox genes and Sox genes are mutated,and this mutation can be inherited from the RCC-L to the GF-L.It was also found that the genetic material from the female KOC and the male BSB was recombined in the RCC-L and the GF-L,and this recombination change from the RCC-L are inherited to GF-L.This provides molecular evidence for the existence of genetic material of the original parent in RCC-L and GF-L in the KOC with BSB distant hybridization line.Eighth,transcriptional sequencing of the liver group of KOC,BSB,RCC-L using the three generation of full-length transcripts of group technology reveals that RCC-L and KOC have 1257 orthologous genes,RCC-L and BSB have 389 orthologous genes and RCC-L and KOC and BSB have 149 orthologous genes.The analysis of the fusion gene shows that there are 52 genes both from common carp and BSB,5 genes both from red crucian carp and BSB,5 genes both from red crucian carp and KOC.This reveals from the transcriptome level that the RCC-L contains genetic material of KOC and BSB.The conclusion of this study is that the homodiploid red crucian carp originates from the distant hybridization pathway between Koi carp and blunt snout bream and the homodiploid red crucian carp self-crossing can generate homodiploid goldfish.