Copy number variation molecular marker influencing pig carcass straight length on pig chromosome 17 and application of copy number variation molecular marker

Abstract

The invention discloses a copy number variation molecular marker influencing the straight length of a pig carcass on a pig chromosome 17 and application of the copy number variation molecular marker. The copy number variation molecular marker is a fragment corresponding to a 15660659bp-15676598bp interval on a chromosome 17 of an international pig reference genome 11.1 version; the copy number of the copy number variation molecular marker affects the carcass straight length of the pig, and the carcass straight length of the pig with the copy number larger than 2 is larger than the carcass straight length of the pig with the copy number equal to 2. The copy number of the copy number variation molecular marker provided by the invention is remarkably related to the carcass straight length character of a pig, the identification of the carcass straight length character can be realized by identifying the copy number of the copy number variation molecular marker, and the carcass straight length of a group can be increased generation by generation by selecting individuals with the copy number greater than 2 in the breeding process, so that the breeding efficiency is improved. The body type of the pigs is improved, and the meat yield of commercial pig groups is increased.

Description

Technical Field

[0001] This invention belongs to the field of molecular biology technology and relates to a molecular marker for copy number variation on pig chromosome 17 that affects the straightness of the pig carcass and its application. Background Technology

[0002] Achieving both high market weight and high lean meat percentage is a crucial goal for commercial pig production in my country. Carcass length refers to the straight-line distance from the anterior edge of the pubic symphysis to the anterior edge of the first cervical vertebra. Carcass length is generally related to the pig's skeletal structure, muscle development, and overall body shape. Measuring carcass length can help predict a pig's growth potential and overall development. Generally, a longer carcass length indicates a larger body size and stronger growth potential. Carcass length is closely related to carcass weight, lean meat percentage, and meat value, directly impacting the economic benefits of pig farming. This makes carcass length a key indicator for measuring pig growth performance and farming efficiency, and an indispensable trait in modern pig breeding.

[0003] Copy number variation (CNV) refers to copy number mutations in submicroscopic (the range resolvable by a conventional electron microscope) segments ranging in size from kb to Mb. These variations, including deletions, duplications, and inversions, are collectively referred to as CNVs, but do not include gene variations caused by transposon insertions and deletions. CNVs are an important mode of genetic variation and have broad application prospects in the breeding of disease resistance and desirable traits in livestock and poultry. They can be used as an effective genetic marker or source of genetic information in livestock and poultry breeding. Summary of the Invention

[0004] The purpose of this invention is to provide a molecular marker for copy number variation on pig chromosome 17 that affects the straightness of the pig carcass and its application.

[0005] According to one aspect of the present invention, a copy number variation affecting the straight length of a pig carcass is provided, specifically a copy number variation corresponding to the segment in the interval 15660659bp-15676598bp on chromosome 17 of the International Pig Reference Genome Version 11.1.

[0006] The copy number variation molecular marker provided by this invention corresponds to a fragment on chromosome 17 in the range of 15660659bp-15676598bp, as shown in SEQ ID NO:1. The copy number of this molecular marker is significantly correlated with the carcass length trait in pigs; specifically, pigs with a copy number greater than 2 have significantly longer carcasses than pigs with a copy number equal to 2. Identifying the copy number of this molecular marker allows for the identification of the carcass length trait in pigs, and selecting pigs with a copy number greater than 2 can accelerate the pig breeding process and achieve genetic improvement in pigs.

[0007] Therefore, the copy number variation molecular marker located on pig chromosome 17 and associated with carcass length provided by this invention can be applied to:

[0008] (1) Identify the straight length trait of the pig carcass;

[0009] (2) Prepare products for identifying the straight length trait of pig carcasses;

[0010] (3) Pig genetic improvement: Pigs with a copy number greater than 2 of the molecular markers affecting the straight length of the pig carcass on chromosome 17 are selected to achieve pig genetic improvement;

[0011] (4) Prepare a product for assisting in the genetic improvement of pigs. This product is based on identifying the copy number of molecular markers on chromosome 17 of pigs that affect the straight length of the pig carcass to assist in the genetic improvement of pigs.

[0012] In some implementations, the pigs are preferably Duroc-Landrace-Large White crossbred pigs, i.e., commercial pigs obtained by crossing Duroc, Landrace, and Large White pigs.

[0013] According to another aspect of the invention, a primer pair is provided, comprising primer pair P1 and primer pair P2.

[0014] Primer pair P1 can specifically amplify the fragment containing the nucleotide sequence shown in SEQ ID NO:2. The nucleotide sequence of the upstream primer is shown in SEQ ID NO:4, and the nucleotide sequence of the downstream primer is shown in SEQ ID NO:5. The nucleotide sequence shown in SEQ ID NO:2 is a specific DNA sequence located in the region 15660659bp-15676598bp on chromosome 17 of the International Swine Reference Genome Version 11.1.

[0015] Primer pair P2 can specifically amplify the fragment containing the nucleotide sequence shown in SEQ ID NO:3. The nucleotide sequence of the upstream primer is shown in SEQ ID NO:6, and the nucleotide sequence of the downstream primer is shown in SEQ ID NO:7. The nucleotide sequence shown in SEQ ID NO:3 is the nucleotide sequence (NC_010457.5) of the porcine glucagon (GCG) gene, which serves as a reference sequence, and it does not exhibit copy number variation.

[0016] According to a third aspect of the present invention, a kit is provided comprising primer pair P1 and primer pair P2.

[0017] The applications of the primer pairs and kits provided by this invention include, but are not limited to:

[0018] (1) Identify the copy number of the molecular markers on chromosome 17 of pigs that affect the straight length of the pig carcass;

[0019] (2) Prepare products for identifying the copy number of molecular markers on chromosome 17 of pigs that affect the straight length of the pig carcass;

[0020] (3) Identify the straight length trait of pig carcasses. The identification of the straight length trait of pig carcasses is achieved by identifying the copy number of molecular markers that affect the copy number variation of pig carcasses on chromosome 17.

[0021] (4) Prepare a product for identifying the straight length of pig carcasses. This product is based on identifying the copy number of molecular markers on chromosome 17 that affect the straight length of pig carcasses to identify the straight length of pig carcasses.

[0022] (5) Pig genetic improvement: Pigs with a copy number greater than 2 of the molecular markers affecting the straight length of the pig carcass on chromosome 17 are selected to achieve pig genetic improvement.

[0023] (6) Prepare a product for assisting in the genetic improvement of pigs, which is based on identifying the copy number of molecular markers on chromosome 17 of pigs that affect the straight length of the pig carcass to assist in the genetic improvement of pigs.

[0024] In some embodiments, the kit provided by the present invention may further include: dNTPs, DNA polymerase, and Mg. 2+ The components of a standard PCR reaction system, including PCR reaction buffer, can be directly referenced or adopted from the relevant components of commercially available PCR amplification kits.

[0025] According to a fourth aspect of the present invention, a method for genetic improvement of pigs is provided, comprising the following steps:

[0026] (1) Determine the copy number of the molecular markers of copy number variation related to carcass length located on chromosome 17 of pigs;

[0027] (2) Select individuals with a copy number greater than 2 of the molecular marker of copy number variation and eliminate individuals with a copy number equal to 2; thereby improving the carcass length of offspring pigs and enhancing their body size and growth potential.

[0028] In some implementations, step (1), determining the copy number of a molecular marker for copy number variation related to carcass length on chromosome 17 of the pig, may include the following steps:

[0029] Whole-genome DNA was extracted from the pigs to be tested, and PCR amplification was performed using primer pair P1 and primer pair P2. The copy number of the copy number variation molecular markers was calculated according to the following formulas (1) and (2):

[0030] ΔΔCt=[(Ct 目标序列 -Ct 参考序列 )] 试验组 -[(Ct 目标序列 -Ct 参考序列 )] 对照组 (1)

[0031] Copy number = 2 × 2 -ΔΔCt (2)

[0032] The nucleotide sequence of the target sequence is shown in SEQ ID NO:2, the nucleotide sequence of the reference sequence is shown in SEQ ID NO:3, the experimental group is the pigs to be tested, and the control group is the pigs with a known copy number variation molecular marker on chromosome 17 that affects the length of the pig carcass equal to 2 (referred to as the known pigs without copy number variation).

[0033] In some implementations, the pigs are Duroc-Landrace ...Handcross hybrids.

[0034] Compared with the prior art, the beneficial effects of the present invention include:

[0035] (1) This invention provides a molecular marker for copy number variation located on chromosome 17 of pigs that is related to the straight length of the pig carcass, and verifies the effect of its copy number on the straight length trait of pigs. This helps to establish a molecular marker-assisted selection breeding technology for rapid improvement of the straight length trait of pigs, improve the breeding process of Duroc-Landrace-Large White crossbred pigs, so as to meet the needs of the breeding pig market, increase the price of breeding pigs, and reduce breeding costs.

[0036] (2) This invention provides a primer pair that can be used to identify the copy number of molecular markers on chromosome 17 of pigs that affect the copy number variation of pig carcass length. Through this primer pair, an efficient and accurate molecular marker-assisted breeding technology can be established to quickly and accurately select traits and accelerate the breeding process. Attached Figure Description

[0037] Figure 1 This is a Manhattan plot of genome-wide association (GWAS) analysis of the straight length trait of pig carcasses on chromosome 17 in Duroc, Landrace, Large White, and Large White three-way crossbred pigs; where: the horizontal axis represents the chromosome number of the pig; the vertical axis represents the -logP value.

[0038] Figure 2 This is a heatmap of normalized Hi-C interaction frequencies, showing changes in the chromatin loop structure at the BMP2 locus; red triangles mark the TAD region containing BMP2 and the copy number variation molecular markers of this invention, and red rhombuses mark the putative chromatin loop structure.

[0039] Figure 3 This is the result of a luciferase reporter gene experiment.

[0040] Figure 4 This is a copy number type detection graph of molecular markers for copy number variation in test samples; where: the horizontal axis represents the ID number of the test sample; the vertical axis represents the copy number type of the molecular markers according to formula 2×2. -ΔΔCt The calculated copy number. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the embodiments. The embodiments are for illustrative purposes only and do not limit the invention in any way. Unless otherwise specified, the raw materials and reagents used in the embodiments are conventional products that can be obtained commercially; experimental methods that do not specify specific conditions in the embodiments are generally performed under conventional conditions in the art or according to the conditions recommended by the manufacturer.

[0042] Example 1: Identification and Verification of CNVs Related to the Straight Length of Pig Carcasses

[0043] (1) Experimental pig herd

[0044] The experimental pig herd used in this invention consisted of 1496 Duroc-Landrace-Large White crossbred pigs from the breeding pig division of Guangdong Wens Foodstuff Group Co., Ltd., with detailed pedigree records. During the rearing process, the pigs had free access to feed and water, and the feeding method and conditions remained consistent throughout, following conventional practices.

[0045] (2) Method for measuring the straight length of the carcass

[0046] After the pigs were raised to a weight of 100±5kg, they were slaughtered and the straight-line distance from the anterior edge of the pubic symphysis to the anterior edge of the first cervical vertebra was measured using a tape measure to obtain phenotypic data of the carcass straight length trait.

[0047] (3) Extraction of porcine genomic DNA

[0048] Ear tissue was collected from 1496 Duroc-Landrace-Large White crossbred pigs. Whole-genome DNA was extracted using the standard phenol-chloroform method. The DNA quality and concentration of each sample were determined using a Nanodrop-ND1000 spectrophotometer. An A260 / 280 ratio of 1.8–2.0 and an A260 / 230 ratio of 1.7–1.9 were considered acceptable. Finally, the acceptable DNA samples were uniformly diluted to approximately 50 ng / μL.

[0049] (4) Pig whole genome variation genotyping

[0050] DNA samples were sent to Beijing Novogene Technology Co., Ltd. for next-generation sequencing, and the sequencing results were in FASTQ format. First, GATK v4.0.2.1 software was used to generate a dict file based on the pig reference genome (Sscrofa11.1). Second, BWA-MEM-0.7.12 software was used to correlate the FASTQ data reads onto the pig reference genome. Third, SAMtools v1.9 software was used to generate a bam file. Fourth, Manta v1.6.0 software was used to detect structural variations, generating VCF files containing data from 1496 Duroc-Landrace-Landrace-Changchun three-way crossbred pigs in this study. Fifth, svimmer v0.1 software was used to merge the VCF files, and graphtyper v2.7.7 software was used to perform population genotyping on the detected structural variations. A total of 92,486 structural variation sites were finally obtained. The obtained genotypic data were quality controlled using PLINK v1.9, removing structural variants with a detection rate <90% and a mimor allelic frequency (MAF) <5%, as well as those located at unknown locations and on sex chromosomes. The remaining 63,623 structural variants and 1,496 samples were used for subsequent data analysis.

[0051] (5) Genome-wide association analysis (GWAS)

[0052] Because kinship and population stratification effects can cause false positives, a kinship matrix needs to be constructed using GCTA software before association analysis. Principal component analysis is then performed using GCTA software, and the first five principal components, measurement field, measurement year, and season are used as covariates to correct for population structure. Finally, GWAS analysis is performed using a univariate mixture model in GCTA software. This invention references the human genome significance threshold, setting the genome significance and chromosome significance thresholds to 5.00E-08 (5.00 × 10⁻⁸). -8 ) and 1.00E-06 (1.00×10 -6 ).

[0053] GWAS analysis results are as follows Figure 1 As shown. From Figure 1 It was found that in Duroc-Landrace-Large White crossbred pigs, there is a significant structural variation on chromosome 17 that affects the straightness of the pig carcass. This variation is a copy number variation, with the strongest associated structural variation being Chr17: 15660659bp-15676598bp (P = 6.05 × 10⁻¹⁰). -23 ).

[0054] (6) Genome capture sequencing analysis

[0055] Porcine intervertebral disc tissue was sent to Wuhan Fraser Genomics Co., Ltd. for genome capture sequencing (Hi-C) to analyze the three-dimensional spatial structure of chromatin. Hi-C sequencing data were processed using Juicer v2.0 software (default parameters). High-quality data were aligned to a reference genome, and sex chromosomes, mitochondrial genomes, and low-quality alignment results (MAPQ < 30) were filtered out. A 10K resolution normalized contact matrix was generated using the Knight-Ruiz algorithm to correct for bias. Furthermore, quantile normalization of inter-sample bias was performed using HiCcompare v1.26.0 software.

[0056] Hi-C results are as follows Figure 2 As shown, the copy number variation that significantly affects the straightness of the pig carcass and BMP2 are located within the same topological association domain (TAD) and exhibit direct chromatin interactions, indicating its role as a cis-regulatory element in circular linkages. Meanwhile, the BMP2 gene has been repeatedly reported to affect vertebral length and lumbar muscle depth.

[0057] Based on the above results, this invention determines that BMP2 is the causal gene affecting the straight length of pig carcasses, and the copy number variation molecular marker located on chromosome 17 in the range of 15660659bp-15676598bp in the International Pig Reference Genome Version 11.1 is the fundamental reason for the changes in the expression level of the BMP2 gene.

[0058] (7) Luciferase reporter gene assay

[0059] Dual-luciferase assays were performed on human and mouse chondrocytes (HUM-iCell-s018, MIC-iCell-s003, Cellverse Ltd.) cultured at 37°C in a 5% CO2 incubator. Chondrocytes were seeded into 48-well plates and co-transfected with a reporter vector and the pRL-TK Renalis luciferase control vector (E2241, Promega). Transfected cells were cultured for 24 hours before lysis. Luciferase activity was measured using a dual-luciferase reporter gene detection system (E1910, Promega). Each construct's reporter assay was independently replicated at least five times. Statistical analysis was performed using t-tests; a p-value less than 0.05 was considered statistically significant.

[0060] Results of luciferase reporter gene assay as follows Figure 3 As shown, higher luciferase activity was observed in chondrocytes transfected with a vector containing a hypothesized enhancer sequence (its nucleotide sequence is shown in SEQ ID NO:1), demonstrating that the copy number variation molecular marker of the present invention can act as an enhancer to stimulate BMP2 gene expression. Previous studies have identified the BMP2 gene as a key growth factor in osteogenic processes. Therefore, it can be determined that the copy number variation molecular marker of the present invention alters chromatin conformation, strengthening the promoter-enhancer loop structure. This alteration induces increased expression of the BMP2 gene in specific tissues, ultimately leading to increased carcass length in pigs.

[0061] (8) Analyze the association between different copy numbers and carcass straightness phenotype to verify the effect of copy number variation molecular markers on carcass straightness traits.

[0062] The results are shown in Table 1. According to Table 1, we can see that:

[0063] 1) The copy number of the molecular marker for copy number variation provided by this invention is significantly correlated with the carcass length trait of pigs (P<0.01), indicating that this molecular marker significantly affects the carcass length trait of pigs. The breeding process of the carcass length trait of pigs can be accelerated by using auxiliary selection of this copy number variation.

[0064] 2) Pigs with a copy number variation molecular marker greater than 2 have significantly longer carcass lengths than pigs with a copy number equal to 2. Selecting individuals with a copy number greater than 2 during the breeding process can progressively increase the carcass length of the population, significantly improving body shape and increasing meat production in the commercial pig population, thus bringing greater economic benefits to enterprises.

[0065] Table 1. Correlation analysis of copy number of molecular markers with copy number variation and carcass length.

[0066]

[0067] (9) Effect analysis

[0068] This invention provides a copy number variation molecular marker that is significantly associated with the carcass length trait in pigs. Using this copy number variation molecular marker for marker-assisted selection can accelerate the carcass length breeding process in pigs. During the breeding process, if individuals with a copy number of 2 for the copy number variation molecular marker affecting carcass length are selected to have a copy number greater than 2, the carcass length of each pig can be increased by 2.35 cm, resulting in higher meat yield and greater economic benefits for enterprises.

[0069] Example 2: Methods for genetic improvement of pigs

[0070] The specific nucleotide sequences of the molecular markers for copy number variations affecting the straightness of the pig carcass on pig chromosome 17 are shown in SEQ ID NO:1. The target sequence (SEQ ID NO:2) is a DNA sequence specific to the 15660659bp-15676598bp region on pig chromosome 17, and the primer pairs (primer pair P1) for its PCR amplification are shown in SEQ ID NO:4 and SEQ ID NO:5. Simultaneously, the pig GCG gene sequence (NC_010457.5) published by NCBI is used as a reference sequence (SEQ ID NO:3), and the primer pairs (primer pair P2) for its PCR amplification are shown in SEQ ID NO:6 and SEQ ID NO:7.

[0071] Primer pair P1 is:

[0072] Upstream primer F1: 5'-TCCGTGTGCAGCCATAAAGT-3' (SEQ ID NO:4);

[0073] Downstream primer R1: 5'-CCAAAGACAGCCCTTCCCAA-3' (SEQ ID NO:5).

[0074] Primer pair P2 is:

[0075] Upstream primer F2: 5'-GAATCAACACCATCGGTCAAAT-3' (SEQ ID NO: 6);

[0076] Downstream primer R2: 5'-CTCCACCCATAGAATGCCCAGT-3' (SEQ ID NO:7).

[0077] The genetic improvement methods for pigs include the following steps:

[0078] S1. Determine the copy number of molecular markers associated with copy number variation in pig carcass length.

[0079] (1) Collect ear tissue from pigs or tail tissue from piglets, extract whole genome DNA from pigs using the standard phenol-chloroform method, and then perform quality testing and concentration determination on the extracted DNA.

[0080] (2) PCR amplification

[0081] Prepare a 10 μL mixture, including: 1 μL DNA sample, 0.3 μL upstream primer, 0.3 μL downstream primer, 5 μL PCR mix, and 3.4 μL ddH2O. The PCR mix can be commercially available 2×Taq PCR Star Mix (Dye) (manufacturer: GenStar, catalog number: A012-101), which includes dNTPs, DNA polymerase, and Mg2+. 2+ Components of conventional PCR reaction systems, such as PCR reaction buffer.

[0082] PCR reaction program: 95℃ pre-denaturation for 10 min, 95℃ denaturation for 10 s, 60℃ annealing for 15 s, 72℃ extension for 20 s, for a total of 40 cycles. Melting curve: 95℃ for 10 s, 65℃ for 1 min, 95℃ for 15 s. Each sample was amplified using primer pairs P1 and P2, with three replicates per primer pair.

[0083] (3) Copy number determination of molecular markers with copy number variation

[0084] The copy number of the molecular marker with copy number variation in the experimental group samples can be estimated based on the difference in Ct values ​​(Cyclethreshold) between the experimental and control groups, by calculating 2×2 -ΔΔCt Copy number variant markers were classified into three categories: reference homozygous genotype, 2×2... -ΔΔCt =2; heterozygous genotype, 2×2 -ΔΔCt =3; homozygous mutant genotype, 2×2 -ΔΔCt =4. The formula for calculating ΔΔCt is: ΔΔCt=[(Ct 目标序列 -Ct 参考序列 )] 试验组 -[(Ct 目标序列 -Ct 参考序列 )] 对照组 Among them, Ct 目标序列 and Ct 参考序列 The Ct values ​​refer to the target sequence (SEQ ID NO:2) and the reference sequence (SEQ ID NO:3), respectively. The test group is the sample to be tested for the presence of copy number variation, and the control group is the known control sample without copy number variation, which can be the sample without copy number variation known in Example 1.

[0085] (4) DNA sequence sequencing identification

[0086] The PCR amplification products were sequenced, with gene fragments sequenced in both forward and reverse reactions. The obtained sequences were compared with the NCBI genome sequence to identify the corresponding copy number variation region (SEQ ID NO:2). The sequencing results are shown below:

[0087]

[0088] Note: The regions marked with underlines are the verified copy number variation regions, and the positions of the designed primer sequences are indicated by bolding at the beginning and end of the sequence.

[0089] GCG gene qPCR amplification sequence (SEQ ID NO:3):

[0090]

[0091] Note: The underlined regions are the amplification regions, and the bolded beginnings and ends of the sequence indicate the locations of the designed primer sequences.

[0092] S2. Select pigs with a copy number greater than 2 for breeding, and cull individuals with a copy number of 2.

[0093] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A molecular marker for copy number variation on porcine chromosome 17 that affects pig carcass length, characterized by: The copy number variation molecular marker is a fragment corresponding to the 15660659bp-15676598bp interval on chromosome 17 of the international pig reference genome version 11.1; the copy number of the copy number variation molecular marker affects the straight length of the pig's carcass, wherein the straight length of the carcass of pigs with a copy number greater than 2 is greater than the straight length of the carcass of pigs with a copy number equal to 2.

2. The copy number variation molecular marker according to claim 1, characterized in that The pig is a Duchangda triple hybrid pig.

3. The use of copy number variation molecular marker according to claim 1 or 2, characterized in that: The applications include: (1) Identify the pig carcass length trait; (2) preparing products for identifying pig carcass length traits; (3) Pig genetic improvement, based on breeding pigs with more than 2 copies of the copy number variation molecular marker on chromosome 17 that affects the vertical length of the pig carcass to achieve genetic improvement of pigs; (4) Prepare a product for assisting pig genetic improvement, wherein the product assists pig genetic improvement based on identifying the copy number of a molecular marker for copy number variation on pig chromosome 17 that affects the length of the pig carcass.

4. A primer pair, characterized in that The primer pair comprises primer pair P1 and primer pair P2, wherein: The primer pair P1 specifically amplifies an amplified fragment containing the nucleotide sequence shown in SEQ ID NO: 2, the nucleotide sequence of the upstream primer is shown in SEQ ID NO: 4, and the nucleotide sequence of the downstream primer is shown in SEQ ID NO: 5; The primer pair P2 specifically amplifies an amplified fragment containing the nucleotide sequence shown in SEQ ID NO: 3, the nucleotide sequence of the upstream primer is shown in SEQ ID NO: 6, and the nucleotide sequence of the downstream primer is shown in SEQ ID NO:

7.

5. The use of the primer pair according to claim 4, characterized in that, The applications include: (1) Identify the copy number of molecular markers on porcine chromosome 17 that affect pig carcass length; (2) preparing a product for identifying the copy number of a molecular marker for copy number variation on porcine chromosome 17 that affects the length of the pig carcass; (3) Identifying the pig carcass length trait, based on identifying the copy number of a copy number variation molecular marker on pig chromosome 17 that affects the pig carcass length trait; (4) preparing a product for identifying the pig carcass length trait, wherein the product realizes the identification of the pig carcass length trait based on identifying the copy number variation molecular marker on pig chromosome 17 that affects the pig carcass length; (5) Pig genetic improvement, based on breeding pigs with more than 2 copies of the copy number variation molecular marker on chromosome 17 that affects the length of the pig carcass; (6) Prepare a product for assisting pig genetic improvement, wherein the product assists pig genetic improvement based on identifying the copy number of a molecular marker for copy number variation on pig chromosome 17 that affects the length of the pig carcass.

6. A kit, characterized in that Its composition includes the primer pair described in claim 4.

7. Use of the kit according to claim 6, characterized in that, The applications include: (1) Identify the copy number of molecular markers on porcine chromosome 17 that affect pig carcass length; (2) preparing a product for identifying the copy number of a molecular marker for copy number variation on porcine chromosome 17 that affects the length of the pig carcass; (3) Identifying the pig carcass length trait, based on identifying the copy number of a copy number variation molecular marker on pig chromosome 17 that affects the pig carcass length trait; (4) preparing a product for identifying the pig carcass length trait, wherein the product realizes the identification of the pig carcass length trait based on identifying the copy number variation molecular marker on pig chromosome 17 that affects the pig carcass length; (5) Pig genetic improvement, based on breeding pigs with more than 2 copies of the copy number variation molecular marker on chromosome 17 that affects the length of the pig carcass; (6) Prepare a product for assisting pig genetic improvement, wherein the product assists pig genetic improvement based on identifying the copy number of a molecular marker for copy number variation on pig chromosome 17 that affects the length of the pig carcass.

8. A method for genetic improvement of pigs, characterized in that: The steps include: (1) determining the copy number of the copy number variation molecular marker according to claim 1 in a pig; (2) Select individuals with a copy number greater than 2 for the copy number variation molecular marker and eliminate individuals with a copy number of 2.

9. The method for genetic improvement of pigs according to claim 8, characterized in that: In step (1), the method for determining the copy number of the copy number variation molecular marker according to claim 1 in a pig comprises the following steps: The whole genome DNA of the pig to be tested was extracted, and PCR amplification was performed using the primer pair according to claim 4. The copy number of the copy number variation molecular marker was calculated according to the following formulas (1) and (2): ΔΔCt=[(Ct 目标序列 -Ct 参考序列 )] 试验组 -[(Ct 目标序列 -Ct 参考序列 )] 对照组 (1) Copy number = 2 × 2 -ΔΔCt (2) The nucleotide sequence of the target sequence is shown as SEQ ID NO: 2, the nucleotide sequence of the reference sequence is shown as SEQ ID NO: 3, the test group is the pigs to be tested, and the control group is the pigs whose copy number of the copy number variation molecular marker according to claim 1 is known to be equal to 2.

10. The method for genetic improvement of pigs according to claim 8 or 9, characterized in that: The pig is a Duchangda triple hybrid pig.

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