Variation Of HBB And MC5R Gene And Their Genetic Effect In Sheep

This study investigated the variation and genetic effect of HBB and MC5 R gene in sheep.In this study,6 Mongolian sheep(Hu sheep,Small-tail Han sheep,Guangling big-tail sheep,Tan sheep,Sunite sheep and Ujmuqin sheep)and 3 Tibetan sheep(Valley-type Tibetan sheep,Oura-type Tibetan sheep and Plateau-type Tibetan sheep)in different environment as research object,SNP loci of HBB and MC5 R gene were detected by mixed DNA sample sequencing technology.Besides,genotyping was performed by direct sequencing,the relationship between SNP loci allele frequency and haplotype frequency of HBB gene and altitude as well as between SNP loci allele frequency and haplotype frequency of MC5 R gene and environmental temperature were analyzed,and the genetic effect of SNP loci genotype and haplotype of two genes on litter size in Hu Sheep were also discussed.In addition,coding sequences of HBB gene of 30 species and MC5 R gene of 36 species were collected from GenBank,and the similarity and phylogenetic relationships of the same gene in different species and the selective direction of these genes were studied,the selection pressure of SNP loci in different populations of sheep was also detected.This study could lay the foundation for further research on HBB and MC5 R gene function,and provide a theoretical basis for the breeding of sheep litter size by using molecular markers of HBB and MC5 R gene.The results of this study are as follows:1.22 SNP loci were detected in HBB gene.Among them,there are 8 nonsynonymous substitutions that is g.1087A>T,g.1088A>C,g.1111C>G,g.1136A>G,g.1162A>G,g.1164G>A,g.1165A>C and g.1247T>A,respectively.16 SNP loci were detected in MC5 R gene,of which there are 6 nonsynonymous substitutions that is g.625C>T,g.1947G>A,g.2028T>A,g.2292G>A,g.2451G>A and g.2478G>A,respectively.2.The selective test between species showed that HBB gene and MC5 R gene were strongly positive selected.9 loci(5A,9A,12 T,50S,52 D,69D,87 Q,116R,125V)in the amino acid sequence encoded by HBB gene and 8 loci(31L,32 H,42E,45 L,47G,51 R,83G,341T)in the amino acid sequence encoded by MC5 R gene were significantly affected by positive selection.3.In Intraspecific groups,the selective test showed that HBB gene g.1164G>A locus which can cause methionine to be replaced with valine was affected by balancing selection;MC5R gene g.2028T>A locus which can cause isoleucine to be replaced with asparagine was affected by strong positive selection.4.By analyzing the relationship between 22 SNP loci allele frequency and haplotype frequency of HBB gene and altitude,the results can be seen that allele frequency of g.1136A>G locus were significantly correlated with altitude(P<0.05),and allele frequency of g.787C>T,g.800G>A,g.809C>G,g.889G>A,g.956C>T,g.957A>G,g.958G>A,g.968T>C,g.1007T>A,g.1020T>A,g.1021C>T,g.1087A>T,g.1088A>C,g.1111C>G,g.1162A>G,g.1165A>C,g.1173C>T and g.1176T>C loci were extremely significant correlated with altitude(P<0.01).In these loci,variations in g.1087A>T,g.1088A>C,g.1111C>G,g.1136A>G,g.1162A>G and g.1165A>C loci leaded to changes in the amino acid sequence.And beyond that frequency of 2 haplotypes that is H1 and H3 in HBB gene was significantly correlated with altitude(P<0.05).5.By analyzing the relationship between 16 SNP loci allele frequency and haplotype frequency of MC5 R gene and year-round average temperature showed that correlation analysis results were all not significant(P>0.05).6.Association analysis of genotype and haplotype of SNP loci of HBB gene and MC5 R gene in Hu sheep with litter size showed that genotype of g.1164G>A locus in HBB gene had a significantly genetic effect on third litter size(P<0.05),GG genotype were higher than GA genotype 0.53 and AA genotype 0.49,respectively,and SNP loci haplotype of HBB gene also had a significantly genetic effect on third litter size(P<0.05).The genetic effect of genotype of MC5 R gene g.2393A>G locus on third litter size were significantly(P<0.05),AA genotype were higher than AG genotype 0.72,but the genetic effect of SNP loci haplotype of MC5 R gene on litter size was not significant(P>0.05).Above all,HBB gene was affected by balancing selection in sheep,and MC5 R gene was positively selected in Mongolian sheep.6 nonsynonymous substitutions in HBB gene which associated with altitude were related to sheep adaptation to high altitude hypoxia environment.The polymorphism of g.1164G>A locus in HBB gene and g.2393A>G locus in MC5 R gene associated with the productive trait.