Yi chuan xue bao = Acta genetica Sinica最新文献

A simple method is presented, which uses a chi2 statistic to measure asymmetry of the substitution matrix between two DNA sequences in order to test a homogeneity hypothesis of the substitution processes. In theory, this chi2 test holds irrespective of whether there is among-site (i) heterogeneity in substitution rates, (ii) correlation in evolutionary rates/models, and (iii) variation in substitution models. Computer simulations showed that the chi2 test is powerful under a variety of models of sequence evolution. Comparison of the eleven sequenced arthropod mtDNAs by using this test revealed that most of the observed evolutionary models were homogeneous between the two mosquitoes but not between Daphnia pulex or Artemia franciscan and the other arthropods, probably due to shifts to a high AT content. A comparison to Kumar and Gadagkar's test by computer simulation as well as empirical data analysis is also given.

A cDNA library (2.1 x 10(6) pfu/mL) was constructed from the oral gland of Lampetra japonica. After random selection of clones for sequencing, 1 323 clones with inserts longer than 100 bp and with good chromato-grams were obtained. Using BlastX and BlastN programs, We found 653 ESTs (49.36%) that shared significant homology with known sequences in protein or nucleotide databases of NCBI, including 328 ESTs homologous to known sequences of Petromazonidae animals. These ESTs were classified into 11 different functional categories,the highest proportion of which was related to protein synthesis. Out of the 1323 ESTs, 162 non-redundant contigs were assembled from 547 sequences after alignment using software at the threshold of more than 90% homology over a minimum of 20 base pairs. There were eight full-length cDNAs with complete open reading frame. Further studies on the ESTs in the library may be helpful to elucidate the components of Lampetra japonica oral gland and to understand the function of those proteins at the molecular level.

The 1 042 bp control region of mitochondrial DNA from 84 geese of 15 domestic goose breeds was sequenced and genetic differentiation was analysed. Results showed that the interpopulation nucleotide divergence was highest (3.805% -4.067%) between Yili and the other 14 breeds. The average nucleotide diversity variation within different domestic breeds was 0 - 0.116%. Excluding the Yili, the interpopulation nucleotide divergence between Huoyan and the remaining breeds, was 0.211% - 0.272%, which was significantly higher than that between any other two breeds (0 -0.094%). During the formation of domestic breeds in China,there is an association between the genetic differentiation of domestic geese and their geographic distribution. The divergence time of Huoyan breed was relatively earlier and genetic drift may have been the main factor to affect the genetic differentiation of the Huoyan breed (Nm = 0.02 -0.54). On the other hand, gene flow is the main reason for the lack of a clear differentiation among the remaining 13 Chinese domestic geese breeds (Nm = 12.0 - 65.33).

Tibet is a center of distribution and differentiation of genus Hordeum in China,and has a great deal of species resource. The sequences of the nontranscribed intergenic spacer (NTS) region of 5S nuclear ribosomal DNA was studied in 18 varieties of the close relative of wild barley (Hordeum spontaneum) from different geographical regions in Tibet and Turkmenistan. These sequences were determined by sequencing the clones of PCR products. Alignment of sequences revealed that the 5S rDNA NTS contained two comparatively conservative regions, A and B, and a variable TAG repeat (V). The number of TAG repeats varies from 4-17, also including several transitions and conversions (TAG-->TCG, TAG-->TAC). The total size of the conservative regions was from 168 -169 bp, and the sequence length variation was only 1 bp. The GC content (%) of the conservative sequence was 43.8% and the homologous of that nearly 98.2% -100%. The number of variable sites was 12 (7.1%). In general, there were more transitions than conversions in the variation sites,and the ratios of transition/conversion were 1.0 - 2.0. NTS polymorphism of 5S rDNA was mainly determined by polymorphism of TAG repeats. The molecular system-tree showed that the NTS should be a useful marker to classify the accessions in Hordeum.

The origin of non-coding sequences, especially introns,is an outstanding issue that has been receiving continuous debate for the last two decades. In the current work we use a mathematical model to characterize DNA sequences and find that the 3-tuple distributions in different reading frames of a given coding sequence differ sharply from each other, while they are almost identical to each other in introns or other non-coding sequences. SREs (Symmetric relative entropies) decrease progressively from coding sequences of primitive prokaryotes to those of advanced eukaryotes and from non-coding sequences of low eukaryotes to those of high eukaryotes with a correlation coefficient of 0.86. In silico evolution experiments show that SREs typical of higher eukaryotic introns can be achieved from prokaryotic coding sequences as the mutation ratio reaches 2/100. The fact that (a total of 25 introns) from all three different genomes S. pombe, C. elegans and H. sapiens searched are found to share high sequence identity with coding regions indicates that at least some introns may have come directly from CDS (coding sequences). We suggest that SREs may be a useful feature for evolutionary study.

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 (P<0.01) and between Dorset sheep and Hu sheep (P <0.05). 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 (P < 0.05) and 0.7 (P < 0.05) 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.

Ankylosing spondylitis (AS) is a highly heritable, common inflammatory rheumatic disease. Since 1970s, evidence has increasingly pointed to HLA-B27 as the major gene involved in susceptibility to AS. However, genome-wide scan and association studies have shown, in addition to HLA, regions outside the HLA are involved in susceptibility to AS. Furthermore, there is compelling evidence that non-B27 genes, either within or outside the HLA, are involved in disease aetiology. This review mainly summarized different genes associated with AS, and the current progress in this exciting area.

In order to understand the genetic contribution of six agronomic traits to yield, 14 flue-cured tobacco varieties (or breeding lines) and their 41 F1 crosses were used for multivariable conditional analysis. The contribution of additive variance of plant height to yield was larger than other agronomic traits. The largest contribution of dominant variance to yield was due to the length of middle leaves. All agronomic traits investigated had small contribution to yield due to additive x environment interaction effects and dominant x environment interaction effects. No identical trait of different parents showed the largest contribution to additive effect of yield. This could be resulted from the fact that each parent had its own genetic and developmental characterization. The dominant effects of yield were mainly influenced by length of middle leaves in most crosses. Length of middle leaves could be served as ameasurement to indirectly select the cross parent having high dominant effect of yield.

In the F2 population crossed from two early stability rice (Oryza sativa L.) with four cultivars, eight uniform strains were recorded. Genetic analysis showed that both uniform strains with uniform agronomic characteristics and segregated strains segregating in Mendelian manner were observed in F2 population of the same combination. Four types of marker-bands were obtained after the F2 uniform strains were marked by 26 ISSR primers:t ype I, maternal marker bands present, and paternal marker bands absent; type II, paternal marker bands present, and maternal marker bands absent; type III, parts of maternal and paternal marker bands present, and the others absent; type IV, new recombined marker bands appeared, and all maternal and paternal marker bands absent. But segregating strains showed heterzygosity marker bands, maternal and paternal marker bands being present. The uniform strains and normal strains in rice might be grouped into two classes on the basis of the 2000 bp marker band amplified by the ISSR marker primers No. 900. This result would provide experimental basis for the study on genetic mechanism of early stability in rice.

In this study, we performed sequentially combined PI and DAPI (CPD) staining and FISH with two different 45S rDNA clones on meiotic pachytene and mitotic metaphase chromosomes in tomato. Ten red CPD bands were shown on eight pachytene bivalents, and 12 bands were shown on six pairs of mitotic metaphase chromosomes. The CPD bands exhibited on mitotic metaphase chromosomes corresponded to the prominent bands exhibited on the pachytene chromosomes. The distinctive CPD bands, which could be constantly and clearly detected using the CPD staining procedure we improved, provided new landmarks for chromosome identification in tomato. FISH with the tomato 45S rDNA clone revealed very strong signal(s) in the satellite(s) on the short arm of chromosome 2 as well as weak signals in five CPD banded regions at pachytene or four pairs of CPD banded regions at metaphase chromosomes. However, FISH with pTa71 plasmid only revealed signals in the satellite. Considering the difference in sequence between the two rDNA clones, we inferred that only the satellite contains the coding regions of 45S rDNA unit in tomato. The property of CPD bands as well as the DNA sequences probably involved in the five CPD banded regions was discussed.