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Prolactin receptor (PRLR) gene was studied as a candidate gene for the prolificacy of Jining Grey goats. Five pairs of primers were designed to detect single nucleotide polymorphisms of exon 10 and part of 3'untranslated region (UTR) of PRLR gene in both high fecundity breed (Jining Grey goat) and low fecundity breeds (Liaoning Cashmere goat, Boer goat and Angora goat) by PCR-SSCP. The nucleotide sequence of exon 10 and part of 3'UTR of caprine PRLR gene was spliced in this study for the first time. The length of this sequence was 1,118 bp. This sequence shared 98.33%, 93.92%, 74.52% homology with the published mRNA of PRLR gene of sheep, cow and human separately, and shared 78.29% homology with the published partial genomic sequence of PRLR gene of the alpaca. Only the products amplified by primers P1, P2, P4 displayed polymorphisms. For primer P1, two genotypes (AA and AB) were detected in both Jining Grey goats and Liaoning Cashmere goats, two genotypes (AA and AC) were detected in Angora goats, and only genotype AA was detected in Boer goats. Sequencing revealed two mutations (186G-->A and 220T-->C) of PRLR gene in the genotype AB in comparison to the genotype AA. The former mutation resulted in an amino acid change of Asp-->Asn, and the latter mutation resulted in an amino acid change of Leu-->Pro. Only one mutation (140A-->G) was found in the genotype AC in comparison to the genotype AA, and this mutation did not cause any amino acid change. The difference of the least squares means (LSM) for litter size between AA and AB was non-significant (P>0.05) in Jining Grey goats. For primer P2, two genotypes (DD and DE) were detected in Jining Grey goats, Liaoning Cashmere goats and Boer goats, and only genotype DD was detected in Angora goats. Sequencing revealed two mutations (52G-->A and 122G-->A) of PRLR gene in the genotype DE in comparison to the genotype DD. The former mutation did not cause any amino acid change, and the latter mutation resulted in an amino acid change of Arg-->Gly. The difference of LSM for litter size between DD and DE was non-significant (P>0.05) in Jining Grey goats. For primer P4, two genotypes (FF and FG) were detected in Jining Grey goats, two genotypes (FF and GG) were detected in Liaoning Cashmere goats, only genotype FF was detected in Boer goats, and three genotypes (FF, FG and GG) were detected in Angora goats. Sequencing revealed one mutation (143A-->G) of PRLR gene in the genotype GG in comparison to the genotype FF, and this mutation resulted in an amino acid change of Met-->Val. The Jining Grey does with genotype FG had 0.76 (P< 0.05) kids more than those with genotype FF. These results preliminarily showed that the PRLR gene is either a major gene that influences the prolificacy of Jining Grey goats or a molecular marker in close linkage with such a gene.

To analyze the structure and function of the melatonin 1b receptor (MT2) in sheep, single nucleotide polymorphisms were detected in exon 2 of sheep MT2 gene using genomic DNA from five sheep breeds by five primers. Polymorphisms were found, and 33 nucleotide mutations were revealed by comparing the mutant types with the wild types. Among them, 14 give rise to deduced amino acid changes. However, none is likely to be associated with nonseasonal or seasonal estrus in sheep breeds tested. Sequence of exon 2 of MT2 of Small Tail Han sheep shows much closer phylogenetic relationship with predicted bovine and porcine MT2 than with human and mouse. The deduced amino acid sequence shows higher identity with the MT2 of cattle (95%) and pig (79%) than with human (76%) and mouse (71%). A rather high identity (61-63%) with the MT1 of sheep, human and mouse was also found. Compared with the other known MT2, 35 unique altered amino acids were revealed. Albeit it also contains a NAXXY motif in transmembrane 7, both a DRY motif and a CYVCR motif were detected just downstream from its third transmembrane domain rather than NRY and CYICH found in other melatonin receptor groups. We presumed that it is possible that the structural changes make its binding function to the ligands attenuated or disrupted, and other genes (most probably MT1) were substituted in the progress of evolution, which ultimately resulted in no detectable expression in current breeds of sheep.

Single nucleotide polymorphism in exon 1 of the estrogen receptor (ESR) gene was detected by PCR-SSCP in both high fecundity sheep breeds (Small Tail Han sheep, Hu sheep and German Mutton Merino sheep) and low fecundity sheep breeds (Dorset sheep,Suffolk sheep). Results indicated that there were three genotypes (AA, AB and BB) in all three high fecundity sheep breeds, but only two genotypes (AA, AB) in both low fecundity breeds. In Hu sheep,German Mutton Merino sheep, Small Tail Han sheep, Suffolk sheep and Dorset sheep,the frequency of allele A was 0.672, 0.786, 0.846, 0.857 and 0.867, respectively, and the frequency of allele B was 0.328, 0.214, 0.154, 0.143, and 0.133, respectively. Sequencing revealed a C--G mutation at 363 bp of exon 1 of ESR gene in the BB genotype in comparison to the AA genotype. The genotype distribution was significantly different between Small Tail Han sheep and Hu sheep (P0.01) and between Dorset sheep and Hu sheep (P0.05). There was no difference in genotype distribution between other sheep breeds. The Small Tail Han sheep ewes with genotypes AB or BB had 0.51 (P0.05) and 0.7 (P0.05) more lambs than those with genotype AA, respectively. These results showed that the estrogen receptor locus is either a major gene that influences the prolificacy in Small Tail Han sheep or in close linkage with such a gene. In view of our results, marker-assisted selection using ESR is warranted to increase litter size in sheep and will be of considerable economic value to mutton producers.

Genetic variation of seven microsatellite loci BM1818, BM1258, BM1443, BM1905, BM302, BM4505 and CYP21 which were closely linked to somatic cell score (SCS) was analyzed in 240 Beijing Holstein cows with nondenaturing polyacrylamide gel electrophoresis. Allele frequencies, heterozygosity, polymorphic information content, the effective number of alleles of seven microsatellite loci were calculated. Relationships between seven microsatellite loci and somatic cell score in Beijing Holstein cows were primarily analyzed by least squares linear model. Least squares means of SCS for BM1818 (284 bp/284 bp), BM1258 (106 bp/92 bp), BM1443 (166 bp/160 bp), BM1905 (187 bp/187 bp), BM302 (142 bp/140 bp), BM4505 (240 bp/236 bp) and CYP21 (215 bp/198 bp) were relatively lower,and their genotypes were the most favorable genotypes in respective locus for mastitis resistance. Least squares means of SCS for BM1818 (286 bp/286 bp), BM1258 (102 bp/102 bp), BM1443 (170 bp/160 bp), BM1905 (197 bp/195 bp), BM302 (154 bp/145 bp), BM4505 (240 bp/238 bp) and CYP21 (204 bp/192 bp) were relatively higher,and their genotypes were the most unfavorable genotypes in respective locus for mastitis resistance. The information found in the present study would be very important for improving mastitis resistance in dairy cattle by marker assisted selection.

Bone morphogenetic protein 15 (BMP15) gene and growth differentiation factor 9 (GDF9) gene which control the fecundity of Belclare and Cambridge ewes were studied as candidate genes on the prolificacy of Small Tail Han sheep. Single nucleotide polymorphism of GDF9 gene and BMP15 gene was detected in both high fecundity sheep breeds (Small Tail Han sheep and Hu sheep) and low fecundity sheep breeds (Dorset sheep, Texel sheep and German Mutton Merino sheep) by PCR-RFLP. The results showed that the G8 mutation (C --T) of GDF9 gene and the B4 mutation (G --T) of BMP15 gene were not detected in five sheep breeds. There was the same B2 mutation (C --T) of BMP15 gene in Small Tail Han sheep as that in Belclare and Cambridge ewes. The same B2 mutation did not exist in other four sheep breeds. Concerning the B2 mutation of BMP15 gene, AA and AB genotypes were detected in Small Tail Han sheep, frequency of A allele was 0. 734, frequency of B allele was 0.266. The BMP15 B2 genotype distributions were high significantly different (P0.001) between Small Tail Han sheep and other four sheep breeds. The ewes with heterozygous mutant AB had 0.62 (P0.01) lambs more than those with wild homozygous type AA in Small Tail Han sheep. These results indicated that the B2 mutation of BMP15 gene had significant effect on the fecundity of Small Tail Han sheep and ruled out the possibility that the fecundity of Small Tail Han sheep was affected by the G8 mutation of GDF9 gene and the B4 mutation of BMP15 gene.

Mapping of quantitative trait loci for some important traits (milk yield, fat percentage, fat yield, protein percentage, protein yield, clinical mastitis and somatic cell count, reproductive performance, productive life,etc.) in dairy cattle was introduced in this review.

In this paper, we briefly introduced the structure, location, sorts, polymorphism of MHC genes in dairy cattle, and introduced the relationships of MHC genes with economic traits (production traits, diseases, et al.).