Molecular marker associated with body fat character of grass carp and application of molecular marker

Abstract

The invention relates to the technical field of grass carp, in particular to a molecular marker associated with body fat traits of grass carp and application. The invention discloses SNPs molecular markers associated with a grass carp FABP3 gene and a body fat character. The SNPs molecular markers are respectively located at the basic group positions of 29945677, 29948389 and 29948502 of a No.19 chromosome of a grass carp reference genome GCF019924925.1. The three SNPs molecular markers are closely associated with body fat traits such as the abdominal fat index, the liver fat content and the muscle fat content of the grass carp. The molecular marker can be applied to molecular-assisted selective breeding of low-fat grass carp strains.

Description

Technical Field

[0001] The present application relates to the technical field of grass carp, and in particular to molecular markers associated with body fat traits of grass carp and their applications. Background Art

[0002] Grass carp (Ctenopharyngodon idellus) is the largest freshwater economic fish in my country, with a farmed output of 5.94 million tons in 2023. With the development of intensive farming models, artificial compound feeds have been widely used. However, in order to reduce feed costs, producers often add excessive amounts of cheap energy feed to save protein feed, resulting in excessive body fat deposition in grass carp, which in turn leads to frequent hepatobiliary syndrome and reduced fish quality.

[0003] Fatty acid binding protein 3 (FABP3) is a member of the intracellular lipid binding protein superfamily. It has a strong affinity for long-chain fatty acids. Its main function is to promote the uptake of fatty acids from the external environment and transport them to the intracellular mitochondria for β-oxidation, thus providing energy metabolism for the cells. FABP3 is widely distributed in myocardium, skeletal muscle, adipocytes and other tissues with high demand for fatty acids. Given that FABP3 plays an important role in fatty acid uptake, intracellular transport and utilization, the association between FABP3 gene polymorphism and body fat traits of grass carp was explored and analyzed, in order to provide technical support for the breeding of low-fat grass carp strains. Summary of the invention

[0004] The present application discloses SNPs molecular markers that associate the FABP3 gene of grass carp with body fat traits, which are located at base positions 29945677, 29948389, and 29948502 of chromosome 19 of the grass carp reference genome GCF_019924925.1. The three SNPs molecular markers are closely associated with body fat traits such as abdominal fat index, liver fat content, and muscle fat content of grass carp. The above molecular markers can be applied to molecular assisted selection breeding of low-fat grass carp strains. To this end, the embodiments of the present application disclose at least the following technical solutions:

[0005] In the first aspect, the embodiments disclose molecular markers associated with grass carp body fat traits, including a nucleotide sequence formed by a single nucleotide G>A mutation at position 29945677 on chromosome 19 of the grass carp reference genome GCF_019924925.1; a nucleotide sequence formed by a single nucleotide G>T mutation at position 29948389 on chromosome 19 of the grass carp reference genome GCF_019924925.1; and at least one of the nucleotide sequences formed by a single nucleotide C>T mutation at position 29948502 on chromosome 19 of the grass carp reference genome GCF_019924925.1.

[0006] In the second aspect, the embodiment discloses a primer set. The primer set includes: a DNA molecule as shown in SEQ ID NO: 1 and 2; and / or a DNA molecule as shown in SEQ ID NO: 3 and 4. The primer set is used to amplify a nucleotide sequence comprising 3 single nucleotide mutation sites in the molecular marker described in the first aspect. In some embodiments, the DNA molecule as shown in SEQ ID NO: 1 and 2 is used to amplify a nucleotide sequence formed by a single nucleotide G>A mutation at position 29945677 of chromosome 19 of the grass carp reference genome GCF_019924925.1. In some embodiments, the DNA molecule as shown in SEQ ID NO: 3 and 4 is used to amplify a nucleotide sequence formed by a single nucleotide G>T mutation at position 29948389 of chromosome 19 of the grass carp reference genome GCF_019924925.1 and a nucleotide sequence formed by a single nucleotide C>T mutation at position 29948502 of chromosome 19 of the grass carp reference genome GCF_019924925.1.

[0007] In a third aspect, the embodiment discloses a kit. The kit includes the primer set described in the second aspect. The kit is a PCR amplification kit, including the primer set described in the second aspect and other reagents for PCR amplification.

[0008] In the fourth aspect, the embodiment discloses a method for screening grass carp individuals with excellent body fat traits using molecular markers. The method comprises: extracting fin genomic DNA of the grass carp to be selected; performing PCR amplification on the genomic DNA using the primer set described in the second aspect; sequencing the PCR amplification product; determining the genotype of the grass carp at position 29945677 of chromosome 19, position 29948389 of chromosome 19 and / or position 29948502 of chromosome 19 of the reference genome GCF_019924925.1 according to the sequencing base peak graph results; judging the breeding value of the grass carp to be selected in terms of body fat traits according to the genotype, and screening out grass carp individuals with low-fat advantage genotypes.

[0009] In some embodiments, the body fat trait includes at least one of body mass, body length, fatness, visceral body index, abdominal fat index, liver fat content and muscle fat content.

[0010] In some embodiments, the genotype at position 29945677 of chromosome 19 of the reference genome GCF_019924925.1 includes GG, GA and AA. Among them, the body weight of individuals with GG, GA and AA genotypes increases successively. The body length of individuals with GG, GA and AA genotypes increases successively. The fatness of individuals with GG, GA and AA genotypes decreases successively. The visceral body index of individuals with GG, GA and AA genotypes decreases successively. The abdominal fat index of individuals with GG, GA and AA genotypes decreases successively. The liver fat content of individuals with AA genotype is lower than that of GG and GA genotypes. The muscle fat content of individuals with AA genotype is lower than that of GG and GA genotypes. In summary, the AA genotype is a dominant genotype for body fat traits of grass carp and can be used for screening low-fat grass carp.

[0011] In some embodiments, the genotype at position 29948389 of chromosome 19 of the reference genome GCF_019924925.1 includes GG, GT and TT. Among them, the visceral index of individuals with the GG genotype is lower than that of the GT and TT genotypes. The abdominal fat index of individuals with the GG genotype is lower than that of the GT and TT genotypes. The liver fat content of individuals with the GG, GT and TT genotypes increases successively. The muscle fat content of individuals with the GG, GT and TT genotypes increases successively. In summary, the GG genotype is a dominant genotype for the body fat trait of grass carp and can be used for screening low-fat grass carp.

[0012] In some embodiments, the genotype at chromosome 19, No. 29948502 of the reference genome GCF_019924925.1 includes CC, CT and TT. Among them, the body weight of individuals with TT, CT and CC genotypes increases successively. The body length of individuals with TT, CT and CC genotypes increases successively. The fatness of individuals with CC genotypes is lower than that of CT and TT genotypes. The visceral body index of individuals with TT, CT and CC genotypes decreases successively. The abdominal fat index of individuals with TT, CT and CC genotypes decreases successively. The liver fat content of individuals with TT, CT and CC genotypes decreases successively. The muscle fat content of individuals with TT, CT and CC genotypes decreases successively. In summary, the CC genotype is a dominant genotype for body fat traits of grass carp and can be used for screening low-fat grass carp.

[0013] In the fifth aspect, the embodiments disclose the use of the molecular marker described in the first aspect, the primer set described in the second aspect, or the kit described in the third aspect in at least one of screening individuals with excellent body fat traits of grass carp and molecular-assisted selection breeding of low-fat grass carp strains. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1The agarose gel electrophoresis diagram of the PCR amplification products of the grass carp FABP3 gene fragment provided in the example. Samples 1-3 are 476 bp target fragments amplified by the forward primer of SEQ ID NO: 1 and the reverse primer of SEQ ID NO: 2; and samples 4-6 are 635 bp target fragments amplified by the forward primer of SEQ ID NO: 3 and the reverse primer of SEQ ID NO: 4.

[0015] Figure 2 This is the grass carp SNP chr19:29945677 typing sequencing peak diagram provided in the example.

[0016] Figure 3 This is the grass carp SNP chr19:29948389 typing sequencing peak diagram provided in the example.

[0017] Figure 4 This is the peak diagram of the grass carp SNP chr19:29948502 typing sequencing provided in the example. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. The reagents not described separately in detail in the present application are all conventional reagents and can be obtained from commercial channels; the methods not described in detail are all conventional experimental methods and can be obtained from the prior art.

[0019] Association analysis between single nucleotide polymorphisms of FABP3 gene and body fat traits in grass carp

[0020] 1. Experimental Materials

[0021] The grass carp used in the experiment were taken from the Fangcun breeding base of the Pearl River Fisheries Research Institute of the Chinese Academy of Fishery Sciences. They were F3 generation breeding lines bred in the same batch and raised in the same pond. 294 individuals were randomly selected for trait association analysis, and body fat trait indicators were accurately measured. At the same time, fin ray samples were cut and stored in anhydrous ethanol at low temperature.

[0022] 2. Genomic DNA Extraction

[0023] A small amount of grass carp fin ray samples were cut and chopped, digested and lysed with proteinase K, and centrifuged to obtain the supernatant; magnetic bead separation technology was used to extract genomic DNA using a fully automatic nucleic acid extractor.

[0024] 3. PCR and SNPs typing

[0025] PCR amplified the target fragment of grass carp FABP3 gene, and the primer sequences are shown in Table 1:

[0026] Table 1 Primer sequence information for PCR amplification of grass carp FABP3 gene fragment

[0027]

[0028] The PCR reaction system is as follows: 1.0 μL of grass carp genomic DNA template, 1.0 μL each of forward and reverse primers, 10 μL of 2× premixed Taq enzyme, and ddH 2 O is supplemented to 20 μL. The PCR reaction program is: pre-denaturation at 94 °C for 60 s; denaturation at 94 °C for 30 s, annealing at 56 °C for 30 s, extension at 72 °C for 40 s, for 32 cycles. After sequencing the PCR amplification products, the genotypes of the grass carp samples to be tested are determined according to the base peak map at the mutation sites.

[0029] 4. Genetic parameter analysis

[0030] The genetic software PopGene is used to calculate the effective number of alleles (Ne), expected heterozygosity (He), and observed heterozygosity (Ho) of SNPs loci in the experimental population, and the Chi-square test is used to estimate the deviation of the population from Hardy-Weinberg equilibrium; the Picalc software is used to calculate the polymorphism information content (PIC). The results are shown in Table 2. All three SNPs loci are moderately polymorphic loci (0.25 < PIC < 0.50), and the loci chr19:29945677 and chr19:29948502 are in Hardy-Weinberg equilibrium (P > 0.05).

[0031] Table 2 Genetic parameter information of three SNPs of grass carp FABP3 gene

[0032] SNP loci Effective number of alleles Expected heterozygosity Observed heterozygosity Polymorphic Information Content Hard-Weinberg equilibrium chr19:29945677 1.6217 0.3840 0.3673 0.3099 0.4556 chr19:29948389 1.1685 0.1445 0.1224 0.1338 0.0083 chr19:29948502 1.9908 0.4985 0.5102 0.3738 0.6876

[0033] 5. Trait association analysis

[0034] Using the SPSS 19.0 statistical software, the multivariate variance analysis module of the general linear model (GLM) is selected to perform a significance test on the genotypes of different SNPs loci and body fat traits.

[0035] Table 3 Association analysis of SNP locus chr19:29945677 and body fat traits

[0036] genotype GG GA AA Number of individuals 164 108 22 Body mass / g 1600.27±158.21 1620.87±159.86 1636.09±216.83 Body length / cm <![CDATA[46.26±1.80 b ]]> <![CDATA[46.75±2.03 ab ]]> <![CDATA[47.40±2.27 a ]]> Fullness <![CDATA[1.62±0.10 a ]]> <![CDATA[1.59±0.11 a ]]> <![CDATA[1.53±0.08 b ]]> Visceral Index 7.87±0.76 7.79±0.83 7.76±0.93 Abdominal fat index 2.21±0.43 2.13±0.49 2.05±0.48 Liver fat content 7.73±3.62 8.03±3.71 7.50±4.13 Muscle fat content <![CDATA[0.20±0.08 ab ]]> <![CDATA[0.22±0.08 a ]]> <![CDATA[0.18±0.07 b ]]>

[0037] As shown in Table 3, the dominant genotype of the body fat trait of the grass carp SNP locus chr19:29945677 is AA. Compared with GG and GA, individuals with the AA genotype not only have good growth performance and slender body shape characteristics, but also have lower body fat trait indexes such as abdominal fat index, liver fat content, and muscle fat content, and can be selected as grass carp individuals with low-fat dominant genotypes.

[0038] Table 4 Association analysis between SNP site chr19:29948389 and body fat traits

[0039]

[0040]

[0041] As shown in Table 4, the dominant genotype of body fat traits at SNP site chr19:29948389 is GG. Compared with GT and TT, GG genotype individuals have significantly lower body fat trait indicators such as visceral index, abdominal fat index, liver fat content and muscle fat content, and can be selected as grass carp individuals with low-fat dominant genotypes.

[0042] Table 5 Association analysis between SNP site chr19:29948502 and body fat traits

[0043] genotype CC CT TT Number of individuals 82 150 62 Body mass / g <![CDATA[1639.11±173.26 a ]]> <![CDATA[1613.23±161.69 ab ]]> <![CDATA[1566.15±147.54 b ]]> Body length / cm <![CDATA[47.08±2.11 a ]]> <![CDATA[46.40±1.82 b ]]> <![CDATA[46.11±1.90 b ]]> Fullness <![CDATA[1.57±0.10 b ]]> <![CDATA[1.61±0.11 a ]]> <![CDATA[1.60±0.10 ab ]]> Visceral Index <![CDATA[7.54±0.86 b ]]> <![CDATA[7.92±0.76 a ]]> <![CDATA[8.00±0.69 a ]]> Abdominal fat index <![CDATA[1.96±0.45 b ]]> <![CDATA[2.22±0.46 a ]]> <![CDATA[2.33±0.36 a ]]> Liver fat content <![CDATA[7.27±3.34 c ]]> <![CDATA[7.88±3.64 b ]]> <![CDATA[8.41±4.15 a ]]> Muscle fat content <![CDATA[0.19±0.07 b ]]> <![CDATA[0.21±0.08 ab ]]> <![CDATA[0.23±0.09 a ]]>

[0044] As shown in Table 5, the dominant genotype of body fat traits at SNP site chr19:29948502 is CC. Compared with CT and TT, individuals with CC genotype not only have good growth performance and slender body characteristics, but also have lower body fat trait indicators such as abdominal fat index, liver fat content and muscle fat content, and can be selected as grass carp individuals with low-fat dominant genotype.

[0045] 6. Application of SNP loci

[0046] Based on the above research, the embodiment further discloses a primer set. The primer set includes: DNA molecules as shown in SEQ ID NOs: 1 and 2; and / or DNA molecules as shown in SEQ ID NOs: 3 and 4. The primer set is used to amplify a nucleotide sequence containing three single nucleotide mutation sites in the molecular marker described in the first aspect.

[0047] In some embodiments, a nucleotide sequence formed by a single nucleotide G>A mutation at position 29945677 of chromosome 19 of the grass carp reference genome GCF_019924925.1 is amplified using a DNA molecule as shown in SEQ ID NO: 1 and 2. In some embodiments, the length of the amplified product is 476 bp, and the single nucleotide G>A mutation at position 29945677 of chromosome 19 of GCF_019924925.1 is located at 301 bp of the amplified product having a length of 476 bp.

[0048] In some embodiments, a DNA molecule as shown in SEQ ID NO: 3 and 4 is used to amplify a nucleotide sequence formed by a single nucleotide G>T mutation at position 29948389 of chromosome 19 of the grass carp reference genome GCF_019924925.1 and a nucleotide sequence formed by a single nucleotide C>T mutation at position 29948502 of chromosome 19 of the grass carp reference genome GCF_019924925.1. In some embodiments, the length of the amplified product is 635 bp, and the single nucleotide G>A mutation at position 29948389 of chromosome 19 of GCF_019924925.1 is located at 384 bp of the amplified product with a length of 635 bp. In some embodiments, the length of the amplified product is 635 bp, and the single nucleotide C>T mutation at position 29948502 of chromosome 19 of GCF_019924925.1 is located at 497 bp of the amplified product with a length of 635 bp.

[0049] The embodiment discloses a kit. The kit includes the primer set. The kit is a PCR amplification kit, including the primer set and other reagents for PCR amplification.

[0050] The embodiment discloses a method for screening grass carp individuals with excellent body fat traits using molecular markers. The method comprises: extracting genomic DNA from grass carp fin rays; performing PCR amplification on the genomic DNA using the primer set; sequencing the PCR amplification product; determining the genotype of the grass carp at position 29945677 of chromosome 19, position 29948389 of chromosome 19 and / or position 29948502 of chromosome 19 of the reference genome GCF_019924925.1 according to the sequencing results; judging the breeding value of the selected grass carp in terms of body fat traits according to the genotype, and screening out grass carp individuals with low-fat advantage genotypes.

[0051] In some embodiments, the body fat trait includes at least one of body mass, body length, fatness, visceral body index, abdominal fat index, liver fat content and muscle fat content.

[0052] In some embodiments, the genotype at position 29945677 of chromosome 19 of the reference genome GCF_019924925.1 includes GG, GA and AA. Among them, the body weight of individuals with GG, GA and AA genotypes increases successively. The body length of individuals with GG, GA and AA genotypes increases successively. The fatness of individuals with GG, GA and AA genotypes decreases successively. The visceral body index of individuals with GG, GA and AA genotypes decreases successively. The abdominal fat index of individuals with GG, GA and AA genotypes decreases successively. The liver fat content of individuals with AA genotype is lower than that of GG and GA genotypes. The muscle fat content of individuals with AA genotype is lower than that of GG and GA genotypes. In summary, the AA genotype is a dominant genotype for body fat traits of grass carp and can be used for screening low-fat grass carp.

[0053] In some embodiments, the genotype at position 29948389 of chromosome 19 of the reference genome GCF_019924925.1 includes GG, GT and TT. Among them, the visceral index of individuals with the GG genotype is lower than that of the GT and TT genotypes. The abdominal fat index of individuals with the GG genotype is lower than that of the GT and TT genotypes. The liver fat content of individuals with the GG, GT and TT genotypes increases successively. The muscle fat content of individuals with the GG, GT and TT genotypes increases successively. In summary, the GG genotype is a dominant genotype for the body fat trait of grass carp and can be used for screening low-fat grass carp.

[0054] In some embodiments, the genotype at chromosome 19, No. 29948502 of the reference genome GCF_019924925.1 includes CC, CT and TT. Among them, the body weight of individuals with TT, CT and CC genotypes increases successively. The body length of individuals with TT, CT and CC genotypes increases successively. The fatness of individuals with CC genotypes is lower than that of CT and TT genotypes. The visceral body index of individuals with TT, CT and CC genotypes decreases successively. The abdominal fat index of individuals with TT, CT and CC genotypes decreases successively. The liver fat content of individuals with TT, CT and CC genotypes decreases successively. The muscle fat content of individuals with TT, CT and CC genotypes decreases successively. In summary, the CC genotype is a dominant genotype for body fat traits of grass carp and can be used for screening low-fat grass carp.

[0055] In some embodiments, the PCR reaction system in 20 μL includes: 1.0 μL of grass carp genomic DNA template, 1.0 μL of forward and reverse primers, 10 μL of 2× premixed Taq enzyme, and the balance of ddHO. 2 O. The PCR reaction program was: 94°C pre-denaturation for 60 s; 94°C denaturation for 30 s, 56°C annealing for 30 s, 72°C extension for 40 s, 32 cycles.

[0056] In some embodiments, after the PCR product is amplified and sequenced, the genotype is determined according to the corresponding bases of the peak graph at the SNPs site. When at least one of the chr19:29945677 site is an AA genotype, the chr19:29948389 site is a GG genotype, and the chr19:29948502 site is a CC genotype, the resulting grass carp individual is considered to be an excellent grass carp strain with a low body fat content.

[0057] The embodiments also disclose the use of the molecular markers described in the above embodiments, the primer sets described in the above embodiments, or the kits described in the above embodiments in at least one of screening individuals with excellent fat traits of grass carp and molecular-assisted selection breeding of low-fat grass carp strains.

[0058] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be covered within the protection scope of the present application.

Claims

1. Molecular markers associated with body fat traits of grass carp, include: The nucleotide sequence formed by a single nucleotide G>A mutation at position 29945677 on chromosome 19 of the grass carp reference genome GCF_019924925.1; The nucleotide sequence formed by a single nucleotide G>T mutation at position 29948389 on chromosome 19 of the grass carp reference genome GCF_019924925.1; and At least one of the nucleotide sequences formed by a single nucleotide C>T mutation at position 29948502 on chromosome 19 of the grass carp reference genome GCF_019924925.

1.

2. A primer set for amplifying a nucleotide sequence comprising three single nucleotide mutation sites in the molecular marker according to claim 1, wherein the primer set include: The DNA molecules shown in SEQ ID NOs: 1 and 2; and / or The DNA molecules are shown in SEQ ID NOs: 3 and 4.

3. The primer set according to claim 2 is used to amplify the nucleotide sequence formed by the single nucleotide G>A mutation at position 29945677 of chromosome 19 of the grass carp reference genome GCF_019924925.1 using the DNA molecules shown in SEQ ID NOs: 1 and 2.

4. The primer set according to claim 2 is used to amplify a nucleotide sequence formed by a single nucleotide G>T mutation at position 29948389 of chromosome 19 of the grass carp reference genome GCF_019924925.1 and a nucleotide sequence formed by a single nucleotide C>T mutation at position 29948502 of chromosome 19 of the grass carp reference genome GCF_019924925.1 using a DNA molecule as shown in SEQ ID NOs: 3 and 4.

5. A kit comprising the primer set according to any one of claims 2 to 4 and other reagents for PCR amplification.

6. Method for screening grass carp individuals with excellent body fat traits using molecular markers, include: Extracting genomic DNA from the fin rays of the selected grass carp; Performing PCR amplification on the genomic DNA using the primer set described in any one of claims 2 to 4; Sequencing the PCR amplification product; Determine the genotype of the grass carp at position 29945677 of chromosome 19, position 29948389 of chromosome 19 and / or position 29948502 of chromosome 19 of the reference genome GCF_019924925.1 according to the sequencing base peak graph result; The breeding value of the selected grass carp in terms of body fat traits is determined according to the genotype, and grass carp individuals with low-fat advantage genotypes are screened out.

7. The method according to claim 6, wherein the body fat trait include: At least one of body weight, body length, fatness, visceral body index, abdominal fat index, liver fat content and muscle fat content.

8. The method according to claim 7, wherein the genotype at position 29945677 of chromosome 19 of the reference genome GCF_019924925.1 includes GG, GA and AA, and optionally, the body weight of individuals with GG, GA and AA genotypes increases successively, optionally, the body length of individuals with GG, GA and AA genotypes increases successively, optionally, the fatness of individuals with GG, GA and AA genotypes decreases successively, optionally, the visceral body index of individuals with GG, GA and AA genotypes decreases successively, optionally, the abdominal fat index of individuals with GG, GA and AA genotypes decreases successively, optionally, the liver fat content of individuals with AA genotype is lower than that of GG and GA genotypes, optionally, the muscle fat content of individuals with AA genotype is lower than that of GG and GA genotypes, and optionally, the AA genotype is a dominant genotype for body fat traits of grass carp and can be used for screening low-fat grass carp. Optionally, the genotype at chromosome 19, No. 29948389 of the reference genome GCF_019924925.1 includes GG, GT and TT. Optionally, the visceral index of the GG genotype individual is lower than that of the GT and TT genotypes. Optionally, the abdominal fat index of the GG genotype individual is lower than that of the GT and TT genotypes. Optionally, the liver fat content of the GG, GT and TT genotype individuals increases in sequence. Optionally, the muscle fat content of the GG, GT and TT genotype individuals increases in sequence. Optionally, the GG genotype is a dominant genotype for the body fat trait of grass carp and can be used for low-fat grass carp screening; Optionally, the genotype at chromosome 19, No. 29948502 of the reference genome GCF_019924925.1 includes CC, CT and TT. Optionally, the body weight of individuals with TT, CT and CC genotypes increases successively. Optionally, the body length of individuals with TT, CT and CC genotypes increases successively. Optionally, the fatness of individuals with CC genotypes is lower than that of CT and TT genotypes. Optionally, the visceral body index of individuals with TT, CT and CC genotypes decreases successively. Optionally, the abdominal fat index of individuals with TT, CT and CC genotypes decreases successively. Optionally, the liver fat content of individuals with TT, CT and CC genotypes decreases successively. Optionally, the muscle fat content of individuals with TT, CT and CC genotypes decreases successively. Optionally, the CC genotype is a dominant genotype for body fat traits of grass carp and can be used for screening low-fat grass carp.

9. Use of the molecular marker according to claim 1, the primer set according to any one of claims 2 to 4, or the kit according to claim 5 in at least one of screening for individuals with excellent body fat traits of grass carp and molecular-assisted selection breeding of low-fat grass carp strains.

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