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Africans' ability to digest milk linked to spread of cattle raising
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[QUOTE]Originally posted by Troll Patrol # Ish Gebor: [QB] More on Allele (T-13910). [QUOTE] Ancient DNA Analysis Reveals High Frequency of European Lactase Persistence Allele (T-13910) in Medieval Central Europe Ruminant milk and dairy products are important food resources in many European, African, and Middle Eastern societies. These regions are also associated with derived genetic variants for lactase persistence. In mammals, lactase, the enzyme that hydrolyzes the milk sugar lactose, is normally down-regulated after weaning, but at least five human populations around the world have independently evolved mutations regulating the expression of the lactase-phlorizin-hydrolase gene. These mutations result in a dominant lactase persistence phenotype and continued lactase tolerance in adulthood. A single nucleotide polymorphism (SNP) at C/T-13910 is responsible for most lactase persistence in European populations, but when and where the T-13910 polymorphism originated and the evolutionary processes by which it rose to high frequency in Europe have been the subject of strong debate. A history of dairying is presumed to be a prerequisite, but archaeological evidence is lacking. In this study, DNA was extracted from the dentine of 36 individuals excavated at a medieval cemetery in Dalheim, Germany. Eighteen individuals were successfully genotyped for the C/T-13910 SNP by molecular cloning and sequencing, of which 13 (72%) exhibited a European lactase persistence genotype: 44% CT, 28% TT. Previous ancient DNA-based studies found that lactase persistence genotypes fall below detection levels in most regions of Neolithic Europe. Our research shows that by AD 1200, lactase persistence frequency had risen to over 70% in this community in western Central Europe. Given that lactase persistence genotype frequency in present-day Germany and Austria is estimated at 7180%, our results suggest that genetic lactase persistence likely reached modern levels before the historic population declines associated with the Black Death, thus excluding plague-associated evolutionary forces in the rise of lactase persistence in this region. This new evidence sheds light on the dynamic evolutionary history of the European lactase persistence trait and its global cultural implications. [...] Two hypotheses have been proposed to explain the origin of LP and its association with dairying: the culture-historical hypothesis [25] and the reverse cause hypothesis [26]. The culture-historical hypothesis posits that the LP allele arose from low frequency through selection in cultures with a long history of dairying. By contrast, the reverse-cause hypothesis holds that the LP allele may have already been common in certain populations due to genetic drift and only these populations would have adopted the cultural practice of dairying. Additional genetic pressures may have existed in arid climates where milk is one of the only clean sources of water [27] or in northern latitudes where, in the absence of vitamin D, the presence of lactose facilitates the absorption of calcium by the intestinal mucosa and thus reduces the risk of rickets and osteomalacia [28]. Rickets and osteomalacia can cause deformation of the pelvis and are leading causes of obstructed labor and consequent maternal mortality and perinatal morbidity in traditional societies without access to modern medical care [29]. Keeping cattle, sheep and goats not only for meat but also for milk provided important advantages for ancient societies. Milk contains high quality fat, protein and sugar and high amounts of calcium [30]. It is a clean liquid that can be converted into a variety of storable products that may have helped prehistoric people survive periods of scarcity [17]. It has been estimated that a prehistoric cow was able to produce 400600 kg of milk in a lactation period of three to four months. Even after subtracting the 250350 kg needed for the raising of a calf, 150250 kg of milk would remain available for human consumption. The caloric content of this milk is almost equivalent to the meat of an entire cow, and it can be exploited multiple times throughout the animal's lifetime [31]. Although archaeological evidence for dairying in prehistoric Europe is scarce, recent zooarchaeological and biomolecular data suggest that dairying was practiced from the very beginning of the Neolithic (ca. 5000 BC) and became more and more important over time [16], [23], [32]. Another line of evidence comes from SNP [13] and microsatellite variation [33] studies that report strong signals of recent positive selection at the C/T-13910 locus. These studies estimate that selective pressure on the allele began 218820650 years BP and 745012300 years BP, respectively, and computer simulations place the origin of the allele at 62568683 years BP in a region between the central Balkans and Central Europe [18]. Previous ancient DNA studies of LP have reported low, but highly variable frequencies for the lactase persistence allele in Neolithic Europe (Figure 1). In a Neolithic Basque population the lactase persistence allele was found in seven out of 26 individuals, of which two were heterozygous and five were homozygous for the LP allele [34]. In a separate study, one Neolithic individual from Sweden was also found to be heterozygous [35]. All other studies reported only homozygous lactase non-persistent genotypes [14], [36], [37]. To date, only one published ancient DNA study has investigated LP prevalence in a post-Neolithic population; in that study on medieval Hungary (ca. AD 9001100), local commoners and foreign conquerors were found to have different LP genotype frequencies [38]. The foreign conquerors (originating from the east) were found to have exclusively lactase non-persistent genotypes, whereas the local commoners exhibited 33% LP genotypes (CT and TT). As modern LP genotype frequencies in the region are >60% today [38], these results imply rapid allele frequency change during the past millennium. [...] Introduction Lactase persistence (LP) is a common genetic trait in many European, African and Middle Eastern populations. In Europe, LP primarily results from a C→T transition located approximately 14,000 bp upstream of the lactase-phlorizin-hydrolase (LCT) gene in intron 9 of the minichromosome maintenance 6 (MCM6) gene on chromosome 2 [1], [2]. A thymine at this locus (T-13910) prevents down-regulation of lactase activity after weaning. In addition to the European C/T-13910 LP SNP, this region also includes four other SNPs associated with LP in Arab (T/G-13915) and African (C/G-13907, T/C-13913, G/C-14010) populations [2][4]. [...] Discussion The European T-13910 LP allele is among the few human genetic variants with evidence of strong recent selection. Nevertheless, the origin and evolutionary history of this allele remains subject to great debate. Previous studies have established that the T-13910 LP allele was largely absent from early European Neolithic farmers, including LBK populations [14], but little work has been conducted on later periods. A study of medieval Hungary found moderate levels of LP in local commoners (33%) ca. AD 9001100, but extrapolating from these results is complicated by the region's history of conquest by lactase non-persistent Asian invaders [38]. This study of the Dalheim cemetery is the first to investigate post-Neolithic LP frequency in western Central Europe, where LP frequencies are >70% today. Recently, it has been speculated that the major population declines associated with the AD 13461352 Black Death epidemics may have impacted allele frequencies in Europe either through selection or drift. Although this discussion has primarily focused on the CCR5-Δ32 allele [40], [41], it raises the question of whether Black Death population losses, reportedly 30% of the entire European population [40], may have also played a role in altering the frequency of other alleles through drift due to population decline. Both direct radiocarbon dating and historical records securely identify the Dalheim cemetery as a pre-Black Death cemetery, allowing pre-epidemic LP frequencies to be measured. The high frequency of C/T-13910 LP genotypes observed in the Dalheim cemetery (72%) falls within the range of LP frequencies reported for present-day Germany and Austria (7180%) and the alleles are in Hardy-Weinberg equilibrium, suggesting allele frequency stability over the last millennium. Thus, there is no evidence of C/T-13910 LP frequency change associated with the Black Death. Additionally, our results suggest that the incomplete selective sweep posited for the T-13910 allele [24] may have reached the present allele frequency in western Central Europe by ca. AD 1200. Conclusion Lactase persistence is a genetic trait enabling life-long digestion of the milk sugar lactose. The ability to rely on ruminant secondary products, such as milk, likely conveyed selective advantage during times of resource scarcity, and genetic lactase persistence has independently evolved at least five times in European, Middle Eastern, and African populations. Previous ancient DNA studies have established that genetic lactase persistence was low or absent in most European Neolithic populations. In this study, we show that the frequency of lactase persistence in medieval Germany (72%) is similar to that found today in Germany and Austria (7180%), suggesting that the incomplete selective sweep of the lactase persistence allele may have reached the present allele frequency in western Central Europe by AD 1200. Although many aspects of the origin and early evolutionary history of the T-13910 LP allele remain uncertain, ancient DNA research has made great strides in narrowing the period of European LP selection to an approximately 4,000 year window spanning 3000 BC to AD 1200. Future ancient studies on this period are likely to reveal the specific evolutionary forces acting on the T-13910 allele and the relationship between dairying and LP genotypes. [/QUOTE]--Annina Krόttli Ancient DNA Analysis Reveals High Frequency of European Lactase Persistence Allele (T-13910) in Medieval Central Europe Published: January 23, 2014DOI: 10.1371/journal.pone.0086251 http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0086251 [/QB][/QUOTE]
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