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Hormone-sensitive lipase (HSL) is the key enzyme responsible for the mobilization of free acids from adipose tissue, and it is also the most important enzyme that affect fat deposition. In this paper, the porcine hormone-sensitive lipase gene 5'-UTR and exon I were sequenced. The sequence number in GenBank are AY332499, AY332497, AY332504, AY332505. A GC-CG in the DNA sequence -13 - -12 bp of porcine HSL gene 5'-UTR was detected between Duroc, Meishan, Qingping pig, Largewhite and Landrace. A G-->A missense mutation was detected in HSL gene exon I of different pig breeds. The characterization of the BsaH I PCR-RFLP polymorphism in exon I of the porcine HSL gene of different breeds and "Largewhite x Meishan" F2 group was analyzed. By association analysis between BsaH I PCR-RFLP polymorphism and GG, GG, AA genotypes of HSL gene exon I, a significant difference of pig eye area was found between AG and GG genotypes (P<0.05) in F2 group.

Porcine uncoupling protein-3 gene was used to study its effect on carcass and meat quality traits. The UCP3 partial translated regions in skeletal muscle from four pig breeds were sequenced and the comparison of the fragment sequences among four pig breeds showed that there were three coding-region single nucleotide polymorphisms (cSNP), of which the mutation at 842 bp of the open reading frame can result in the amino acid chang between methionine and threonine, so we selected the mutation as polymorphic site. The detection of polymorphic fragment by the technique of single strand conformation polymorphism (SSCP) and chi2 analysis among three pig breeds indicated that the distribution of three genotypes(AA, AB and BB) was significantly different between Meishan and Large White or Meishan and Landrace( P < 0.01). In addition, association analysis of UCP3 polymorphism with carcass and meat quality traits was conducted in the F2 generation from the Large White x Meishan resource family, the results with GLM analysis showed that UCP3 polymorphism has significant effect on several carcass and meat quality traits and also additive effect on some carcass and meat quality traits predominated in the resource family. It implied that UCP3 gene could be a candidate gene locus or a linked marker to a major gene, which affects the porcine carcass traits and meat quality traits significantly.

To search for the chromosome regions for quantitative trait loci (QTL) affecting meat quality in pigs, a three-generation resource family was developed in China using three Large White grand sires and seven Meishan grand dams. A total of 147 F2 progenies derived from two populations in 1998 (n = 81) and 2000 (n = 66) were phenotyped for meat quality. All animals were typed for 48 microsatellite markers covering six chromosomes: 1, 2, 3, 4, 6 and 7. Linear model and least square analyses were used for interval mapping meat quality in jointed population and single population, permutation for empirical threshold. The strongest linkage at chromosome-wide level (P < 0.01) and genome-wide level (P < 0.05) on chromosome 4 affecting intramuscular fat (IMF) QTL from the population in 2000 was detected with explained phenotypic variance of 5.24%, and Meishan's QTL increased the intramuscular fat content. There was a suggestive QTL for IMF near the threshold of chromosome-wide in the same region in jointly population. The QTL for pH value in m. Semispinalis Capitis and m. Biceps Femoris were located on chromosomes 1 and 3, respectively. One and three QTL affecting WHC reached the thresholds of chromosome-wide level in the populations of 1998 and 2000, respectively. In the population of 1998, QTL for moisture content at chromosome-wide level was on SSC6 and in jointed populations were on SSC2, 6 and 7. There were imprinting effects in moisture content QTL, and Meishan and Large White pigs all had favorable effects influencing moisture on different chromosomes.

Genotypes of 24 microsatellite loci were assayed in total of 139 F2 finishing pigs from resource population(Large White x Meishan) in the present study. There were not significant correlation in sex, family and microsatellite loci effects on birth weight (BW), average daily gain (ADG), adjusted weight of 180 d (LWT180), relative growth rate (RGR) and kleiber ratio (KR). Individual gene heterozygosity (Hi) was estimated by using 24 microsatellites. The 139 individuals were classified into five clusters based on Hi by stepwise 0.05 and the traits mentioned above were compared between Hi levels. Birth weight decreased significantly from gene heterozygosity level 1(0.5101 Hi and 1.5185 kg) to level 2(0.5796 Hi and 1.3063 kg, P < 0.05), the difference was 0.2123 kg equal to 14.66% of population average birth weight (1.4479 kg). And then the birth weight increased significantly with the gene heterozygosity increasing (P < 0.05). There were nonlinear relationships between LWT180, ADG, RGR, KR and individual gene heterozygosity, and mostly like the pattern of sinusoidal curve. The peaks were located at about heterozygosity level 2(averagely Hi 0.5796). ADG, RGR and KR at heterozygosity level 2 were significantly higher than level 4(28.7 g/d, 0.0375 and 0.0003 respectively, P < 0.05). The differences were equal 7.38%, 3.99% and 2.20% to respective average population values.

The mutations of ESR, PRLR and FSHR genes were investigated by SNP; 103 F2 sows were slaughtered and their reproductive organs were determined; the litter size of sow was recorded. The linkage between mutations of genes and size of reproductive organ, litter size was analyzed. The results revealed: these sows that could provide more piglets with bigger reproductive organs usually carried genotype like as genotype BB on the sites of ESR, FSHRB and the genotype AA on the sites of ESRB and PRLR, that is, the genotype of BB on the sites of ESR or FSHRB in sow was not only helpful to promote growth of reproductive organs, but also benefit to improve litter size; The size of productive organs and litter size of the sow with genotype AA on the sites of ESRB or PRLR were significantly higher than those of sow with genotype AB or BB.

An intercross between Meishan and Large White pig population was used to map quantitative trait loci(QTL) for protein percentage in muscle. In the present study, all 135 F2 animals, their parents and their grandparents were genotyped for 24 microsatellites, which were in 1, 2 and 6 chromosome. The marker genotypes were used to calculate the additive and dominant coefficients at fixed position in the genome of each F2 animal, and the protein percentage were regressed on to the coefficients in intervals of 1 cM. Three significant QTLs effects were found for protein percentage in muscle. They were located between markers Sw1332 and Sw2130 at chromosome 1, between Sw2516 and Sw1201 at chromosome 2 and between Sw322 and Sw607 at chromosome 6(P < 0.05), and the explained residual variance were 0.91%, 12.76% and 4.60%, respectively. The results show that QTLs, which affect protein percentage, may be located in different chromosomes.

The development of molecular biology techniques and the application of these techniques to farm animals have progressed rapidly and have opened new vistas for investigators wishing to identify genes that control quantitative traits. Now that a comprehensive map has been developed for the porcine genome, genomic scans to detect quantitative trait loci (QTL) can begin. In order to locate the genetic regions in the swine genome that are responsible for economically important traits, a resource population was developed by intercross with three Large White and seven Meishan pigs. In subsequent generations, 66 F2 offsprings in 2000 were recorded for four growth traits including birth weight (BWT), body weight at 60 day (WT60), average daily gain from birth to 60 day (ADG1) and average daily gain from 60 day to the end of test (ADG2), and genotyped for 48 microsatellite markers spanning six chromosomes. Association analyses were performed using interval mapping by regression under an outbred line-cross model on chromosomes 1, 2, 3, 4, 6 and 7. The F threshold values were determined by permutation. A total of 12 QTL were detected at suggestive level for the four traits evaluated in this study. Of the 12 suggestive QTL, 3 and 1 QTL were significant at the chromosome-wise and genome-wise levels. There was a QTL for ADG2 at genome-wide level on chromosome 4 explained additive variance 2.19%. A chromosome-wide QTL affecting ADG1 and WT60 were detected on chromosomes 2 and 1 explained additive variance 0.01% and 26.01%, respectively.

Myostatin(MSTN) gene is expressed specifically in developing and mature skeletal muscle, and the expression products of MSTN gene inhibits muscle growth and differentiation. The polymorphism of the porcine MSTN gene was researched by PCR-SSCP. The SSCP was found in the MSTN gene exon 2 and exon 3. It showed three genotypes (CC, CT, TT) in exon 2 and two genotypes (AG, GG) in exon 3 in Large White pigs. The relationship between polymorphism in exons 2 and 3 and productive performance was analysed. Variance analysis showed that there was no significant relationship between the polymorphism in exon 2 and productive performance. But t test showed that there was a significant relationship between the polymorphism in exon 3 and back fat thickness (P < 0.05), there was also a relationship between the polymorphism in exon 3 and lean meat percentage, but not significant (P > 0.05). The fragments with SSCP polymorphism in exon 2 and 3 were sequenced, the sequencing results showed that there were two single nucleotides mutation, i.e. A-->G at 1008 (exon 3) and G-->T at 480 (exon 2). Two mutations did not change the amino acid but brought an Apa I site in exon 3, and PCR-RFLP molecular marker technique was established with Apa I.

One of the major determining factors in the price of market hogs today is backfat depth. Therefore, identification of regions of the genome affecting this trait is necessary. Gene-mapping technologies have provided scientists the necessary reagents to conduct genomewide searches for genes affecting any phenotype determined in part by the genetic makeup of the animal. Over the past few years, several experimental crosses have been used to detect quantitative triat loci (QTL) for fatness and meat quality traits in pigs. In an intercross between Large White and Meishan pigs, 81 F2 progenies in 1998 were slaughtered and phenotyped for fat deposite traits. F2 animals, their parents, and their grandparents were typed for molecular markers covering chromosomes (SSC) 1,2,3,4,6 and 7, since previous studies had revealed QTL affecting fatness traits on these chromosomes. Linear model and least square analyses were used for mapping these traits. Furthermore, a QTL accounting for imprinting effects was used. A total of 14 QTL at chromosome-wide level were detected on SSC1, 3-4, 6 and 7 for 12 fatness traits. There were evidences for imprinting effects on SSC7 for four traits at 60 cM and nearby. There were QTL for average backfat thickness (BFT) on SSC1, 4 and 7. Among them, BFT QTL on SSC1 and 7 may be the common locus for Sus scrofa. QTL for internal fat percentage was on SSC7 and QTL for average sidefat on SSC6.

The study constructed the genetic linkage map of porcine chromosome 2 and further analysis of quantitative trait loci was conducted. The results of the study demonstrated that all 7 microsatellite loci we chose were with relatively high polymorphism, and its polymorphic information content was from 0.40182 to 0.58477. The genetic map we constructed for resource family was 152.9 cM in length, with the order of all loci highly consistent with the USDA map. All marker intervals were longer than USDA map with the interval between marker Sw2516 and Sw1201 as an exception. Furthermore, we conducted QTLs locating analysis by combining the genetic map with the phenotypic data. QTLs affecting lively estimated traits such as lean meat percentage, were located at 60-65 cM on chromosome 2, while QTLs for the height and marbling of Longissmus dorsi muscle were located at 20 cM and 55 cM, respectively Among them, QTL for estimated lean meat percentage was significant at chromosome-wise level (P < 0.01) and was responsible for 21.55% of the phenotypic variance. QTLs for the height and marbling of Longissmus dorsi muscle were responsible for 10.12% and 10.97% of the phenotypic variance, respectively. The additive and dominance effect of lively estimated traits were in the inverse tendency, while the QTL for the height of Longissmus dorsi muscle had its additive and dominance effect in the same tendency and was with advantageous allele in Large White. The QTLs we detected had relatively large effect on phenotype and built a basis for molecular marker assisted selection and breeding.

A three-generation family of pigs has been constructed by using three Large White boars and seven sows of Meishan pigs as parents. In this family, five F1 males and twenty-three F1 females were intercrossed to generate 147 F2 offspring. According to the pig linkage map of USDA-MARC, eight and nine microsatellite markers selected on chromosomes 1 and 3 were chosen to span the entire chromosomes. The members of this family were genotyped. The characterization of these microsatellites was shown that they were polymorphic and could be used to construct linkage map and detect quantitative trait loci (QTLs). Linkage analyses were performed using the CRI-MAP software package. The lengths of the sex-averaged linkage map were 182.3 cM and 180.2 cM on chromosomes 1 and 3, respectively. There were some differences between the linkage maps in this study and of USDA-MARC. The linkage map of chromosome 1 in female was found to be shorter than in male, and the contrary was on chromosome 3.

Hormone sensitive lipase (HSL) is a key enzyme in fat metabolism. The polymorphism of the pig HSL gene is studied in this paper. The SSCP (Single Strand Conformational Polymorphism) is found in the HSL gene Exon 8. It shows three genotypes (MM, MN, NN). Fat-type pig breeds of Meishan and Tongcheng pigs have more allele M, with frequencies of 0.690 M and 0.740 M, respectively; however, lean-type pig breeds of Landrace and the Large White pigs have more allele N, with frequencies of 0.847 N and 0.845 N, respectively. PCR fragments representing HSL genotypes MM and NN are sequenced. Two A-->G transitions are detected, and it resulted in corresponding changes of amino acid (Asn-->Asp and Glu-->Gly) in the HSL protein, respectively. The HSL gene can be considered as a candidate gene for fatness in pigs.