Genomewide Pattern of Synonymous Nucleotide Substitution in Two Complete Genomes of Mycobacterium tuberculosis

Comparison of the pattern of synonymous nucleotide substitution between two complete genomes of Mycobacterium tuberculosis at 3,298 putatively orthologous loci showed a mean percent difference per synonymous site of 0.000328 ± 0.000022. Although 80.5% of loci showed no synonymous or nonsynonymous nucleotide differences, the level of polymorphism observed at other loci was greater than suggested by previous studies of a small number of loci. This level of nucleotide difference leads to the conservative estimate that the common ancestor of these two genotypes occurred approximately 35,000 ago, which is twice as high as some recent estimates of the time of origin of this species. Our results suggest that a large number of loci should be examined for an accurate assessment of the level of nucleotide diversity in natural populations of pathogenic microorganisms

A multilocus assay reveals high nucleotide diversity and limited differentiation among Scandinavian willow grouse (Lagopus lagopus)

<p>Abstract</p> <p>Background</p> <p>There is so far very little data on autosomal nucleotide diversity in birds, except for data from the domesticated chicken and some passerines species. Estimates of nucleotide diversity reported so far in birds have been high (~10^-3) and a likely explanation for this is the generally higher effective population sizes compared to mammals. In this study, the level of nucleotide diversity has been examined in the willow grouse, a non-domesticated bird species from the order Galliformes, which also holds the chicken. The willow grouse (<it>Lagopus lagopus</it>) has an almost circumpolar distribution but is absent from Greenland and the north Atlantic islands. It primarily inhabits tundra, forest edge habitats and sub-alpine vegetation. Willow grouse are hunted throughout its range, and regionally it is a game bird of great cultural and economical importance.</p> <p>Results</p> <p>We sequenced 18 autosomal protein coding loci from approximately 15–18 individuals per population. We found a total of 127 SNP's, which corresponds to 1 SNP every 51 bp. 26 SNP's were amino acid replacement substitutions. Total nucleotide diversity (<it>π</it>_<it>t</it>) was between 1.30 × 10^-4and 7.66 × 10^-3(average <it>π</it>_{<it>t </it>}= 2.72 × 10^-3± 2.06 × 10^-3) and silent nucleotide diversity varied between 4.20 × 10^-4and 2.76 × 10^-2(average <it>π</it>_{<it>S </it>}= 9.22 × 10^-3± 7.43 × 10^-4). The synonymous diversity is approximately 20 times higher than in humans and two times higher than in chicken. Non-synonymous diversity was on average 18 times lower than the synonymous diversity and varied between 0 and 4.90 × 10^-3(average <it>π</it>_{<it>a </it>}= 5.08 × 10^-4± 7.43 × 10³), which suggest that purifying selection is strong in these genes. <it>F</it>_STvalues based on synonymous SNP's varied between -5.60 × 10^-4and 0.20 among loci and revealed low levels of differentiation among the four localities, with an overall value of <it>F</it>_ST= 0.03 (95% CI: 0.006 – 0.057) over 60 unlinked loci. Non-synonymous SNP's gave similar results. Low levels of linkage disequilibrium were observed within genes, with an average r²= 0.084 ± 0.110, which is expected for a large outbred population with no population differentiation. The mean per site per generation recombination parameter (ρ) was comparably high (0.028 ± 0.018), indicating high recombination rates in these genes.</p> <p>Conclusion</p> <p>We found unusually high levels of nucleotide diversity in the Scandinavian willow grouse as well as very little population structure among localities with up to 1647 km distance. There are also low levels of linkage disequilibrium within the genes and the population recombination rate is high, which is indicative of an old panmictic population, where recombination has had time to break up any haplotype blocks. The non-synonymous nucleotide diversity is low compared with the silent, which is in agreement with effective purifying selection, possibly due to the large effective population size.</p

Detection of sequence polymorphisms in red junglefowl and White Leghorn ESTs

The definitive version is available at www.blackwell-synergy.comOver 16 000 high quality expressed sequence tags (ESTs) from red junglefowl (RJ) and White Leghorn (WL) brain and testis cDNA libraries were generated. Here, we have used this resource for detection of single nucleotide polymorphisms (SNPs), and also completed full-length sequencing of 46 pairs of clones, representing the same gene from both the RJ and WL libraries. From the main set of ESTs, which were assembled using Phrap, 746 putative SNPs were identified, of which 76% were transitions and 24% were transversions. A subset of SNPs was evaluated by sequence analysis of five RJ and five WL birds. Nine of 12 SNPs were verified in this limited sample, suggesting that a majority of the putative polymorphisms documented in this study represent real SNPs. During full-length sequencing of the 46 RJ/WL clones 100 SNPs were identified, which translated to a frequency of 1.90 SNPs/1000 bp. The number of transitions and transversions were 77% and 23%, respectively, and the proportion of non-synonymous vs. synonymous SNPs was 20% and 80%, respectively. Four large insertions/deletions were identified between the RJ and WL full-length sequences, and they appear to represent different splice variants

DNA variation in a 13-Mb region including the F9 gene: inferring the genealogical history and causal role of a hemophilia B mutation (IVS 5+13 A -> G)

About 5.5% of all UK hemophilia B patients have the base substitution IVS 5+13 A-->G as the only change in their factor (F)IX gene (F9). This generates a novel donor splice site which fits the consensus better than the normal intron 5 donor splice. Use of the novel splice site should result in a missense mutation followed by the abnormal addition of four amino acids to the patients' FIX. In order to explain the prevalence of this mutation, its genealogical history is examined. Analysis of restriction fragment length polymorphism in the 21 reference UK individuals (from different families) with the above mutation showed identical haplotypes in 19 while two differed from the rest and from each other. In order to investigate the history of the mutation and to verify that it had occurred independently more than once, the sequence variation in 1.5-kb segments scattered over a 13-Mb region including F9 was examined in 18 patients and 15 controls. This variation was then analyzed with a recently developed Bayesian approach that reconstructs the genealogy of the gene investigated while providing evidence of independent mutations that contribute disconnected branches to the genealogical tree. The method also provides minimum estimates of the age of the mutation inherited by the members of coherent trees. This revealed that 17 or 18 mutant genes descend from a founder who probably lived 450 years ago, while one patient carries an independent mutation. The independent recurrence of the IVS5+13 A-->G mutation strongly supports the conclusion that it is the cause of these patients' mild hemophilia