| This study investigated the genetic diversity and structure of the Bashang long-tailed chicken population at different time periods using mtDNA D-loop region as the experimental object.The characteristics of early muscle fibers of Bashang long-tailed chickens were also measured and analyzed in order to provide reliable basis for the effective protection and utilization of genetic resources of Bashang long-tailed chickens.The main results are as follows:1.The length of mtDNA D-loop region of Bashang long-tailed chicken is between1231-1232 bp,with a missing C base at position 852 in 1231 bp compared to 1232 bp.The content of four nucleotides A,T,C,and G in Bashang long-tailed chicken conservation populations A,T,C,and G is basically the same at three different time periods,accounting for 26.6-26.7%,33.4-33.5%,26.5-26.6%,and 13.3-13.4%,respectively.The A+T content is 60-60.2%,and the G+C content is 39.8-40%,showing bias.A total of 46 polymorphic sites were found in mtDNA D-loop region,including35 different haplotypes,including 36 parsimony informative sites and 10 singleton variable sites.Among them,41 polymorphic sites belong to transitions between bases,and 5 polymorphic sites belong to base replacements.2.By analyzing the level of genetic diversity,it was found that the haplotype diversity（Hd）of the protected population of Bashang long-tailed chicken was 0.949,the average number of nucleotide differences（K）was 8.36232,and the nucleotide diversity（Pi）was 0.00679 in 2016;Hd was 0.950,K was 8.77636,and Pi was 0.00713in 2018;Hd was 0.957,K was 8.87327,and Pi was 0.00721 in 2021.There was no significant difference in the genetic diversity level of the protected population among the three periods,indicating that the conservation effect was good.According to Tajima’s D test results,the test values of the protected population in the three periods were not significant（P>0.1）,conforming to the neutral mutation model,indicating that the population has maintained a relatively stable size in the recent period.By analyzing the Bashang long-tailed chicken population and the local chicken population together,73 different haplotypes were found.Network clustering and phylogenetic tree construction of these 73 haplotypes showed that there were four maternal origins in the protected population of Bashang long-tailed chicken.3.From the 6th embryonic stage,muscle cells gradually gathered and fused,and the muscle fiber contour was initially formed at the 14th embryonic stage,and the muscle fiber contour was clear and distinct at the 17th embryonic stage.The muscle fibers of the chest and leg muscles have the same growth and development rules.From the 14th embryonic stage,the diameter of muscle fibers gradually increased,and the density of muscle fibers gradually decreased.The diameter of chest muscle fibers increased from 3.49±0.91μm at the 14th embryonic stage to 4.38±0.98μm at the 21st embryonic stage,an increase of about 25.5%;while the diameter of leg muscle fibers increased from 3.26±0.50μm at the 14th embryonic stage to 5.35±1.59μm at the 21st embryonic stage,an increase of about 64.11%.The density of chest muscle fibers decreased from 83662.68±8542.39 roots·mm-2 at the 14th embryonic stage to42483.54±345.31 roots·mm-2 at the 21st embryonic stage,a decrease of about 49.22%;while the density of leg muscle fibers decreased from 89292.49±45279.21 roots·mm-2at the 14th embryonic stage to 22986.18±3574.08 roots·mm-2 at the 21st embryonic stage,a decrease of about 74.26%.The change in leg muscle fibers was much greater than that in chest muscle fibers,indicating that the leg muscles developed faster.By observing the chest and leg muscle smears of 1,7,and 14-day-old chicks,it was found that the development of muscle tissue was reflected in the growth of muscle segment length and diameter.The chest muscle segment increased from 6.62±0.64μm at 1-day-old to 7.52±0.84μm at 14-day-old,an increase of about 13.6%;while the leg muscle segment increased from 5.94±0.87μm at 1-day-old to 7.32±0.33μm at 14-day-old,an increase of about 23.23%.The change in leg muscle segment was still greater than that in chest muscle segment,indicating that the leg muscles developed faster. |
