Sequencing And Analysis Of Complete Mitochondrial Genome Of F1 Generation Of Commom Carp × Blunt Snout Bream And F1 Backcrossing Progeny

More and more studies showing that new species formed by distant hybridization among species is one of the important way to promote species diversity.It has been speculated that at least 25%of plants and10%of animals in nature have had distant hybridization events.Distant hybridization can bring the genomes of different species together,which results in large changes in the genotypes and phenotypes of their offspring.Effective distant hybridization and backcrossing can gradually infiltrate the genetic materials of a species into another species,leading to the formation of new species.Once these newly formed species establish a genetically stable fertile strain,they will have important value in biological evolution and genetic breeding.In this study,the hybrid mirror carp（F₁generation of female Cyprinus carpio×male megalobrama amblycephala,2n=100）was used as the female parent,and the backcross test was carried out with the Megalobrama amblycephala as the male parent.A new type homodiploid carassius auratus-like（MCRC）and a new type homologous diploid red crucian carp-like（MRCC）were obtained in the F₁generation.The MCRC and MRCC were very similar to those existed species-wild diploid crucian carp（Carassius auratus,CRC,2n=100）from appearance.In order to further verify their evolutionary relationship between those two new type spicies with wild crucian carp,we sequenced and analyzed the mitochondrial genomes of the two new type crucian carp species,and then the structural sequences of the two crucian carp-like species of MRCR and MRCC are compared with the corresponding parts of their parents and wild crucian carp（CRC）.The main analysis contents are as follows:1.The structural characteristics of the original parental carp（COC）,blunt snout bream（BSB）,hybrid mirror carp（GMCC）,MCRC,MRCC and wild carp（CRC）mitochondrial genome were analyzed and compared,including the location and length of mitochondrial genes,the space and overlap between genes,and the start and stop codons of protein-coding genes,etc.The results showed that the structure of the carp was similar to that of MCRC and MRCC,and The MRCC and wild carp have the highest mitochondrial structure similarity.2.By using of various bioinformatics analysis software,the mitochondrial genome protein encoding genes of various species were analyzed and compared,including amino acid usage and relative synonymous codon usage（RSCU）,etc.The aim was to explore the genetic relationship between MCRC,MRCC and wild carp from the compositional characteristics of the protein-coding genes.3.The non-coding regions of the mitochondrial genome of each species were analyzed and compared,and the relationship between MCRC,MRCC and wild carp was estimated by using the characteristics of the fast evolution rate of the control regions in the non-coding regions.4.The secondary structure of r RNA and t RNA were predicted by using an online tool.It was found that the RNA structure of each species was basically the same,and the base differences were mostly concentrated in the loop region of the secondary structure,and the stem region was relatively conservative.5.The sequence similarity of the complete sequence of mitochondrial genes and each gene fragment were compared to determine the genetic relationship between COC,MCRC,MRCC and wild carp.6.The phylogenetic relationship between the above species was further verified by using the nucleotide sequence and amino acid sequence of the mitochondrial protein-coding gene Cytb,the control region gene sequence and 16S r RNA to construct a phylogenetic tree,that is,MCRC and MRCC are closely related to CRC,and the genetic relationship between the MRCC and the CRC is the closest.Since the original parent of the MCRC and MRCC is the COC,the mitochondrial gene sequences of MCRC,MRCC and the COC are similar,and they have a high similarity to the CRC.Then it is assumed that the CRC can be generated by the crossing between COC and another speicies,and it is also a possible way to generated CRC by crossing between GMCC and BSB.