Abstracts (first author)
Investigating the co-evolution between human lactase gene and dairy culture in Europe
Genes that have undergone recent positive selection during human evolution can provide new insights into the evolutionary forces that have shaped our species. Human lactase gene LCT which encodes the enzyme responsible for hydrolysis of lactose, the milk sugar is under recent positive selection. The production of lactase is declined after the weaning period; however, in some individuals, lactase expression persists into adulthood. Lactase persistence is found at high frequency in northern and western European populations. Based on Principal Component Analysis (PCA) of genetic diversity of six markers in cattle milk protein genes, Beja-Pereira et al. (2003) proposed that since Neolithic times, there has been co-evolution between LCT in humans and cattle milk protein genes. To test this hypothesis, we used dense SNP datasets for human (441,845 SNPs) and cattle (44,706 SNPs) populations to investigate the signatures of positive selection at LCT and cattle milk protein genes in Europe. To this end, we used a new genome-scan method based on a diffusion approximation for the distribution of allele frequency at migration-selection-drift equilibrium (Vitalis et al, in prep). For LCT, we detected a north-south gradient for the intensity of positive selection. For the cattle data, we could not detect any signature of positive selection in cattle milk protein genes. Furthermore, PCA was performed using the markers surrounding cattle milk protein genes provided the same pattern of geographical variation as with the complete cattle genomic data, showing a north-south gradient of variation across Europe. The results of our study therefore provide no evidence for the co-evolution of lactase and cattle milk protein genes. We argue that the coincidence between the gradient in the selection intensity at LCT in humans and geographic variation in cattle genes simply reflect the migration history of both species during the Neolithic along the Danubian route.