Synonymous codon usage varies considerably among Caenorhabditis elegans genes. Multivariate statistical analyses reveal a single major trend among genes. At one end of the trend lie genes with relatively unbiased codon usage. These genes appear to be lowly expressed, and their patterns of codon usage are consistent with mutational biases influenced by the neighbouring nucleotide. At the other extreme lie genes with extremely biased codon usage. These genes appear to be highly expressed, and their codon usage seems to have been shaped by selection favouring a limited number of translationally optimal codons. Thus, the frequency of these optimal codons in a gene appears to be correlated with the level of gene expression, and may be a useful indicator in the case of genes (or open reading frames) whose expression levels (or even function) are unknown. A second, relatively minor trend among genes is correlated with the frequency of G at synonymously variable sites. It is not yet clear whether this trend reflects variation in base composition (or mutational biases) among regions of the C.elegans genome, or some other factor. Sequence divergence between C.elegans and C.briggsae has also been studied.

When the neutral theory of molecular evolution [ 11 was first proposed, silent (that is, synonymously variable) sites in codons were considered to be ideal candidates for truly neutral evolution [Z]. However, as the DNA sequences of numerous genes were determined, it became apparent that the usage of alternative codons for different amino acids was neither uniform nor random. Furthermore, codonusage patterns were found to vary both among species and among genes from the same genome [ 31. This non-random codon usage was interpreted as evidence of selective differences between codons. Codon selectionThe first species in which patterns of codon usage were elucidated was Escherichia coli, with critical evidence coming from knowledge of the abundance, and anticodon sequence, of the various tRNAs present in the cell [4]. Optimal codons were identified as those best recognized (1) by the most abundant tRNAs (2). Highly expressed genes have a highly biased codon usage, with a very high frequency of the optimal codons, while lowly expressed genes have a more random codon usage [4, 51. To illustrate point (Z), consider the six codons for arginine. These are translated by three tRNAs: one (decoding CGU, CGC and CGA) is one of the most abundant tRNAs in E. coli; the other two are of minor abundance, and are rarely

The Turkic language was introduced in Anatolia at the start of this millennium, by nomadic Turkmen groups from Central Asia. Whether that cultural transition also had significant population-genetics consequences is not fully understood. Three nuclear microsatellite loci, the hypervariable region I of the mitochondrial genome, six microsatellite loci of the Y chromosome, and one Alu insertion (YAP) were amplified and typed in 118 individuals from four populations of Anatolia. For each locus, the number of chromosomes considered varied between 51-200. Genetic variation was large within samples, and much less so between them. The contribution of Central Asian genes to the current Anatolian gene pool was quantified using three different methods, considering for comparison populations of Mediterranean Europe, and Turkic-speaking populations of Central Asia. The most reliable estimates suggest roughly 30% Central Asian admixture for both mitochondrial and Ychromosome loci. That (admittedly approximate) figure is compatible both with a substantial immigration accompanying the arrival of the Turkmen armies (which is not historically documented), and with continuous gene flow from Asia into Anatolia, at a rate of 1% for 40 generations. Because a military invasion is expected to more deeply affect the male gene pool, similar estimates of admixture for female-and male-transmitted traits are easier to reconcile with continuous migratory contacts between Anatolia and its Asian neighbors, perhaps facilitated by the disappearance of a linguistic barrier between them. Am J Phys

We typed 1801 males from 55 locations for the Y‐specific binary markers YAP, DYZ3, SRY10831 and the (CA)n microsatellites YCAII and DYS413. Phylogenetic relationships of chromosomes with the same binary haplotype were condensed in seven large one‐step networks, which accounted for 95% of all chromosomes. Their coalescence ages were estimated based on microsatellite diversity. The three largest and oldest networks undergo sharp frequency changes in three areas. The more recent network 3.1A clearly discriminates between Western and Eastern European populations. Pairwise Fst showed an overall increment with increasing geographic distance but with a slope greatly reduced when compared to previous reports. By sectioning the entire data set according to geographic and linguistic criteria, we found higher Fst‐on‐distance slopes within Europe than in West Asia or across the two continents.

The spread of agriculture that started in the Near East about 10 000 years ago caused a dramatic change in the European archaeological record. It is still unclear if that change was caused mostly by movement of people or by cultural transformations. In particular, there is disagreement on what proportion of the current European gene pool is derived either from the pre-agricultural, paleolithic and mesolithic people, or from neolithic farmers immigrating from the south-east. To begin to characterise the mtDNA gene pool of prehistoric Europe we examined five human remains from the Eastern Italian Alps, dated between 14 000 and 3000 years ago. Three of them yielded sufficient amount of mtDNA for analysis. DNA extracts were prepared in two independent laboratories, and PCR products from the first hypervariable segment of the mtDNA control region were cloned and sequenced. Together with the 5200 year old 'ice man', these DNA sequences show that European mtDNA diversity was already high at the beginning of the neolithic period. All the neolithic sequences have been observed in contemporary Europeans, suggesting genealogical continuity between the neolithic and present-day European mtDNA gene pool. The mtDNA sequence from a 14 000 year-old specimen was not observed in any contemporary Europeans, raising the possibility of a lack of continuity between the mesolithic and present-day European gene pools.