Genetics of lactase persistence fresh lessons in the history of milk drinking article pdf available in european journal of humangenetics 3. The evolutionary genetics of lactase persistence in africa. Our data show that the t910 variant is found on two different, highly divergent. The evolution of lactase persistence humans are relatively unique among mammal species in that some of their adult population retains the ability to digest lactose, a sugar found in milk.
Article genetic origins of lactase persistence and the spread of pastoralism in africa alessia ranciaro, 1, michael c. Evolution of lactase persistence royal society publishing. The ability to digest dietary lactose is associated with lactase persistence lp in the intestinal lumen in human. Many people in populations that have a long history of dairying have the trait of lactase persistence. This genetically determined trait differs in frequency worldwide and is due to cisacting. Age estimates based on the intraallelic microsatellite. It is thought that selection has played a major role in maintaining. Resequencing of a second phenotyped cohort revealed the presence of many variant alleles at the locus, the occurrence of which is significantly higher in persistent individuals. Author summary most adults worldwide do not produce the enzyme lactase and so are unable to digest the milk sugar lactose. Lactose intolerance is when a person has symptoms due to a decreased ability to digest lactose, a sugar found in dairy products. Pdf lactose digestion and the evolutionary genetics of. A putative causal nucleotide change has been identified and occurs on the background of a very extended haplotype that is frequent in northern europeans, where lactase persistence is frequent.
Likewise, the cultural practices of dairying and milk drinking have. Clearly, the availability of fresh animal milk created an environment that selected for lactase persistence. It follows a mendelian autosomal heritance regulated by cisacting elements of the lactase gene lct. Lactase, the enzyme responsible for milk digestion, is expressed in the small intestine of nearly all neonate mammals, and normally downregulates following weaning.
Key words milk, polymorphism, population distribution, developmental decline, functional dna element s abstract the enzyme lactase that is. As a primary factor in human evolution, natural selection is an important component of genetic research. When natural selection favors a beneficial allele, such as the lactasepersistence allele red band, that allele is more likely to be passed on from one generation to the next. Some have argued for the culturehistorical hypothesis. The enzyme lactase that is located in the villus enterocytes of the small intestine is responsible for digestion of lactose in milk. Sarah tishkoff and colleagues investigated lactase persistence in east africa. As expected, lactase persistence is strongly correlated with the dairying history of the population.
Lactose digestion and the evolutionary genetics of lactase persistence. Lactase persists into adult life in some, but not all, people. Babies always made lactase, the enzyme that breaks down this. Evidence of stillongoing convergence evolution of the. Just 10,000 years ago, no one past infancy could digest milk sugar, called lactose. Combining genetics, chemistry, and anthropology, this story provides a compelling example of the coevolution of human gene regulation and human culture. The frequency of this allele rose rapidly in europe after transition from huntergatherer to agriculturalist lifestyles and the introduction of milkable domestic species from anatolia some 8000 years ago. Genetics of lactase persistence fresh lessons in the history of milk drinking edward hollox 1 european journal of human genetics volume , pages 267 269 2005. A worldwide correlation of lactase persistence phenotype. Since lactases only function is the digestion of lactose in milk, in most mammal species, the activity of the enzyme is dramatically reduced after weaning. Lactose digestion and the evolutionary genetics of lactase persistence article pdf available in human genetics 1246. This is considered a classical example of geneculture coevolution, and several studies suggested that the lactase gene has been under strong directional evolutionary selective. However, some individuals maintain high enzyme amounts and are able to digest lactose into adulthood i. Population genetics of lactase persistence and lactose.
In some human populations, though, lactase persistence has recently evolved as an adaptation to the consumption of nonhuman milk and dairy products beyond. Pdf lactose digestion and the evolutionary genetics of lactase. Lactase persistence is the continued activity of the enzyme lactase in adulthood. Current estimates for the age of lactase persistenceassociated alleles bracket those for the origins of animal domestication and the culturally transmitted practice of dairying. However, the mechanism and evolutionary significance of this variation have proved more elusive, and continue to excite the interest of investigators from different disciplines. Lactase persistence behaves as a dominant trait because half levels of lactase activity are suf. Tishkoff1,9 in humans, the ability to digest lactose, the sugar in milk, declines after weaning because of. A news article on the search for a lactose tolerance mutation in. Ingram cj, mulcare ca, itan y, thomas mg, swallow dm. The evolutionary genetics of lactase persistence in seven ethnic. Lactase persistence, the ability to digest the milk sugar lactose in adulthood, is highly associated with a t allele situated,910 bp upstream from the actual lactase gene in europeans. Studies of lactase persistence suggest that positive. In other healthy humans, lactase activity persists at a high level throughout adult life, enabling them to digest. Lactose is the main carbohydrate disaccharide sugar in animal milk, including.
Convergent adaptation of human lactase persistence in africa and europe. Iran has a long history of pastoralism and the daily consumption of dairy products. Both genetic changes occur in the regulatory region of the lactase gene. The lactase nonpersistence phenotype is common in adult humans 65%, ingram et al. The levels of haplotype diversity within the lineages defined by two singlenucleotide polymorphisms snps. Lactase persistence is common in people of european ancestry as well as some african, middle eastern and southern asian groups, but is rare or absent elsewhere in the world. Here, we analyzed the background of the alleles carrying the critical variant in 1,611 dna samples from 37 populations. Lactase persistencethe ability of adults to digest the lactose in milkvaries widely in frequency across. They express lactase and can consume fresh milk throughout life. Milk is rich in lactose roughly 40 gramsliter for cows milk, which serves as the major carbohydrate energy source for infants and young animals. This dominantly inherited genetic trait is known as lactase persistence.
Some humans, however, continue to produce lactase throughout adulthood, a trait known as lactase persistence. This trait is likely to have conferred a selective advantage in individuals who consume appreciable amounts of unfermented milk. Genetic diversity of lactase persistence in east african. Lactose digestion and the evolutionary genetics of lactase. Genetics of lactase persistence fresh lessons in the history of milk drinking edward hollox 1 european journal of human genetics volume. In the first column, the red band indicates a genetic variant or mutation associated with lactase persistencethe lactasepersistence allele. Lactase activity is high and vital during infancy, but in most mammals, including most humans, lactase activity declines after the weaning phase. Those affected vary in the amount of lactose they can tolerate before symptoms develop.
Lactose digestion and the evolutionary genetics of lactase persistence ingram from npb npb 2 at university of california, davis. Series of studies revealed five regulatory variants that are located in the 14 kb upstream of lct in. Symptoms may include abdominal pain, bloating, diarrhea, gas, and nausea. These symptoms typically start thirty minutes to two hours after eating or drinking milkbased food.
One of these is at particularly high frequencies in europeans and several others have been found elsewhere. Evidence for selection overview this activity focuses on the genetic changes that gave rise to lactase persistence an example of recent human evolution. A kidfriendly description of sarah tishkoffs genetic studies from the university of maryland. Genetic origins of lactase persistence and the spread of. The origin of lactase persistence coincides with a cultural shift in human populations who began to use the milk of other mammals as food. Pdf genetics of lactase persistence fresh lessons in. The distribution of these different lactase phenotypes in human populations is highly variable and is controlled by a polymorphic element cisacting to the lactase gene. Understanding the genetics of lactase persistence is vital to knowing how it is inherited between populations. Primary research open access the evolutionary genetics of lactase persistence in seven ethnic groups across the iranian plateau hadi charati1,2, minsheng peng1,2,3, wei chen4, xingyan yang5, roghayeh jabbari ori6, mohsen aghajanpourmir7,8, ali esmailizadeh1,6 and. Microsatellite variation and evolution of human lactase. However, most people in europe and many from other populations continue to produce lactase throughout their life lactase persistence.
Lactase persistence and milk consumption in europe an. Nonpersistence or persistence of lactase expression into adult life being a polymorphic trait has been attributed to various single nucleotide polymorphisms in the enhancer region surrounding. The enzyme, lactase, is restricted to the small intestine where it digests lactose in the milk of suckling mammals. The mutation leading to lactase persistence in this population is different from the one found in lactasepersistent individuals from europe. Kotze,5 muntaser ibrahim,6 thomas nyambo,7 sabah a. Hirbo,1 wenya ko, 10 alain froment,2 paolo anagnostou,3,4 maritha j. Lactase persistence is one of the clearest examples of niche construction in humans.
The evolutionary genetics of lactase persistence in africa and the middle east. The ability of adult humans to digest the milk sugar lactose lactase persistence is a dominant mendelian trait that has been a subject of extensive genetic, medical and evolutionary research. Pdf the evolutionary genetics of lactase persistence in. The genetic basis of lp has been investigated in many populations in the world. A snp in the gene encoding lactase lct ct910 is associated with the ability to digest milk as adults lactase persistence in europeans, but the genetic basis of lactase persistence in. A singlenucleotide variant, ct910, located 14 kb upstream of the lactase gene lct, has been shown to be completely correlated with lactase persistence lp in northern europeans. Lactose intolerance lactase nonpersistence lactose intolerance is a deficit in the ability to digest lactose, and is due to a relative lack of the lactase enzyme in the small intestine. The frequency of this allele rose rapidly in europe after transition from huntergatherer to agriculturalist lifestyles and the introduction of milkable.
Genetics of lactase persistence and lactose intolerance. Lactase persistence and milk consumption in europe an interdisciplinary approach involving genetics and archaeology michela leonardi ag palaeogenetik, institute of anthropology, johannes gutenberg university, mainz, d human evolutionary ecology group, department of anthropology, university college london, london, uk m. Lactase persistence lp is a trait in which lactose can be digested throughout adulthood, while lactase nonpersistence lnp can cause lactose intolerance and influence dairy consumption. This activity focuses on the genetic changes that gave rise to lactase persistence an example of recent human evolution. In humans, the ability to digest lactose, the sugar in milk, declines after weaning because of decreasing levels of the enzyme lactasephlorizin hydrolase, encoded by lct.
Lactase persistence is a genetic trait, which varies in frequency in different populations of the world. Lp is prevalent in europe, with the highest frequencies in the northwest of the continent 0. Students explore the evidence for lactasepersistence mutations that arose within the last. Lactase persistence lp, the dominant mendelian trait conferring the ability to digest the milk sugar lactose in adults, has risen to high frequency in central and northern europeans in the last 20,000 years. Nearly every allele associates with an independent haplotype, providing strong evidence that multiple unrelated evolutionary events gave rise to lactase persistence. Persistence of lactase into adulthood varies in frequency worldwide and is attributable to several different single nucleotide changes in an enhancer of the lct gene. Absence of the lactasepersistenceassociated allele in. Lactose intolerance is inherited in an autosomal recessive pattern, that means that one copy of the lactase persistence allele is enough to confer the ability to digest lactose as an adult. Genetic diversity in human populations is the result of a relatively recent biological and cultural evolution, so that most of the human genetic background can be. It has been known for some 40 years that lactase production persists into adult life in some people but not in others. Convergent adaptation of human lactase persistence in. Lactase persistence, the ability to drink milk as an adult and the opposite of lactose intolerance, is a trait that arose in humans as a direct result of our domestication of other mammals.
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