Genetic Analysis Of Polydactyly Traits In Houdan Chicken And Testcross Offsprings And Its Candidate Gene Expression

The Houdan is an old French breed of domestic chicken,it has an unusual butterfly-shaped comb,and is one of few breeds to have five toes rather than the usual four.Since 2003,Houdan chicken was introduced into China,most related researches which are mainly focused on the hybridization effect,production performance and nutrition needs,however,there are few reports on polydactyly traits of Houdan chicken.Therefore,the genetic analysis and gene expression of polydactyly traits in Houdan chicken were performed in this study,it was the purpose of this study to obtain further information on genetics of polydactylism in the fowl.Firstly,three cross combination tests(four-five toes ?× four-five toes ?,four-five toes ?×five-five toes ?,five-five toes ?× five-five toes ?)were designed with different toe-numbers type,and the testcross was carried out to determine the genetic law of polydactyly traits in Houdan chickens.Secondly,Houdan chicken polydactyly was analyzed by polydactyly single nucleotide polymorphisms marker of Chinese native chickens.Thirdly,the Head,Body and Limb tissue expression of six candidate genes(Lmbr1,SHH,RNF32,NOM1,MNX1,GLI3)were analyzed by real-time PCR methods in Houdan chicken.The main results are as followings:1.The results of Houdan Chicken Hybrid with different toe-numbers type showed that four-five toes ? × four-five toes ? combination group has better hatchability but lower birth weight than those of other two groups(P<0.05).The ratio of a polyphalangyls to non-polyphalangyls of four-five toes ?× four-five toes ?group was 3.67:1,and that fit dominant theoretical ratio(3:1)using the Chi Squared Test(P<0.05).And the ratio of other two groups did not fit theoretical ratio.And polyphalangyls penetrance of three groups was 78.57%,77.70%,90.58%,respectively.2.The results of testcross showed that the NO.1-7 cocks were polyphalangyls heterozygous and should be eliminated.The polyphalangyls penetrance of NO.8 and NO.9 cocks were 87.50%,94.11%,they may be polyphalangyls homozygous and can be used for group expansion.The polyphalangyls trait relative to the four toes isdominant inheritance,but with different penetrations.3.SNP molecular markers showed that Lmbr1 gene C4645 A locus for polydactyly traits can accurately detected different toe genotypes of Lushi chicken,Gushi chicken and Silky Fowl,and this SNP can be completely associated with polydactyly traits.However,the SNP cannot detect the polydactyly genotype of the Houdan chickens.This suggests that its polydactyly trait may be controlled by another molecular marker.4.The results of candidate genes expression showed that the Lmbr1,SHH,MNX1 gene decreased first and then increased and the expression of RNF32,NOM1,Gli3 decreased gradually in the head tissue of embryonic development.In the body tissue,the range of expression of candidate genes was small except that the 9th day expression level of Lmbr1 gene was increased significantly(P<0.05).In the limb tissue,candidate gene expression trends were consistent,there was a lower expression level of RNF32,NOM1,Lmbr1,Gli3 and RNF32 gene in the 8th day in limb tissue than those of the 7th day and the 9th day(P<0.05).The expression of SHH gene had been very lower.So,the limb tissue was the main tissue for the formation of polyphalangyls trait,and the developmental period may be the 7th-9th day of embryonic development in Houdan chicken.In Summary,the results showed that polyphalangyls trait of Houdan chicken was autosomal dominant inheritance,but the penetrance of polyphalangyls was different;the offspring of four-four toes may be caused by genetic modification of genes,or may be the result of polygenic regulation.SNP molecular markers(Lmbr1 gene C4645 A locus)can not detect the polydactyly genotype of the Houdan chickens,the polydactyly molecular markers of Houdan chicken still need to do further study.In limb tissue of Houdan,candidate gene expression trends were consistent.It was speculated that the early embryonic development upon polydactylism was in limb bud tissue,and the developmental period may be the 7th-9th day of embryonic development in Houdan chicken.