Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. Farming News .




FARM NEWS
Penn team links Africans' ability to digest milk to spread of cattle raising
by Staff Writers
Philadelphia PA(SPX) Mar 16, 2014


Penn's Sarah Tishkoff administers a lactose tolerance test to a group of Maasai people in Tanzania. The test measures the ability to digest milk -- a trait that Tishkoff and other researchers link with the practice of pastoralism. Image courtesy University of Pennsylvania

Humans' ability to digest milk stems from the advent of cattle domestication in Africa
London, UK (SPX) Mar 14 - Most people lose the ability to digest the milk sugar lactose after weaning, but some populations retain high levels of an enzyme called lactase, which allows them to break down lactose in adulthood. In a study published March 13th in the American Journal of Human Genetics, researchers identified genetic factors associated with lactase persistence in African populations and found that this trait became more prevalent in recent history in conjunction with the introduction and spread of cattle domestication in Africa. The findings provide strong evidence that lactase persistence evolved in human populations as a dietary adaptation.

"To date, there has never been a large-scale study of lactase persistence that included such a large set of geographically and ethnically diverse populations," says study author Sarah Tishkoff of the University of Pennsylvania. "Our study sheds light on both the genetic basis and evolutionary history of a biologically relevant trait in humans and the origins of pastoralism in Africa."

Individuals with northern European ancestry, as well as African, Arabian, and Central Asian pastoral populations with a tradition of fresh-milk production and consumption, retain high levels of lactase into adulthood. DNA sequence variations linked to lactase persistence have been identified in European populations, but until recently, little was known about genetic factors associated with this trait in African pastoral populations.

In the new study, Tishkoff, along with Alessia Ranciaro, also of the University of Pennsylvania, and collaborators around the globe sought to address this gap in knowledge. The researchers performed a large-scale sequencing analysis of all of the genomic regions thought to influence the activity of the lactase-encoding LCT gene in 819 individuals from 63 diverse African populations and in 154 non-Africans from nine different populations in Europe, the Middle East, and Central and East Asia. They identified several single-nucleotide variants-DNA sequence variations affecting a single nucleotide-associated with lactase persistence.

Moreover, their genetic analysis revealed strong evidence of recent positive selection affecting several variants associated with this trait in African populations, most likely in response to the cultural development of pastoralism. The origins of these variants coincided with the introduction of cattle domestication in Africa about 10,000 years ago and its subsequent spread through pastoral migrations. Tishkoff will present an overview of genetic variation in Africa and discuss these findings as well as research about the genetic basis of complex traits, such as short stature in Pygmies, at the Cell Symposium "Evolution of Modern Humans: From Bones to Genomes," which will take place March 16-18 in Sitges, Spain.

Babies are born with the ability to digest lactose, the sugar found in milk, but most humans lose this ability after infancy because of declining levels of the lactose-digesting enzyme lactase. People who maintain high levels of lactase reap the nutritive benefits of milk, however, offering a potential evolutionary advantage to lactase persistence, or what is commonly known as lactose tolerance.

A new study led by University of Pennsylvania researchers - constituting the largest investigation ever of lactase persistence in geographically diverse populations of Africans - investigated the genetic origins of this trait and offers support to the idea that the ability to digest milk was a powerful selective force in a variety of African populations which raised cattle and consumed the animals' fresh milk.

The research was led by Alessia Ranciaro, a postdoctoral fellow in Penn's Department of Genetics in the Perelman School of Medicine, and Sarah Tishkoff, a Penn Integrates Knowledge Professor with appointments in Penn Medicine's Department of Genetics and the School of Arts and Sciences' Department of Biology.

The paper will be published March 13 in the American Journal of Human Genetics.

Previous research had shown that northern Europeans and people with northern European ancestry, as well as populations from Africa, the Arabian Peninsula and Central Asia with a tradition of fresh milk production and consumption, continue to express the lactase enzyme into adulthood.

Some of these earlier studies had traced the genetic origin of this trait in Europeans to a particular mutation that regulates the expression of the gene that codes for lactase. And in 2007 a study by Tishkoff, Ranciaro and colleagues examined African populations and found three addition genetic variants associated with lactase persistence that had not been previously identified.

"But these variants didn't completely account for the reason why some Africans were able to digest milk," Ranciaro said.

To try to reconcile these apparent discrepancies between genotype, the genetic basis of a characteristic, and phenotype, the characteristic itself, Ranciaro, along with colleagues, led field studies to often-remote areas of Kenya, Tanzania and Sudan to collect blood samples and perform a lactose tolerance test on people from diverse ethnic backgrounds.

"The idea was that we wanted to sample as many populations, and as diverse a set of populations, as possible," Ranciaro said. "We included pastoralists, agro-pastoralists, agriculturalists and hunter-gatherers, so the four major subsistence patterns were all covered."

The Penn researchers worked with African collaborators and local district offices and tribal chiefs to spread the word and recruit volunteers for their study.

"This was a very challenging test to do in the field in remote regions," said Ranciaro. "We were careful to make sure that people understood why we were doing this study and that they would need to commit to the hour or more of time needed to do the test."

The test reveals whether someone has the ability to digest lactose into glucose and galactose. It requires participants to fast overnight, have their blood sugar measured, then drink a sweet beverage containing the equivalent lactose of one to two liters of cow's milk and subsequently have their blood sugar tested at set intervals.

To look for genetic variations among the populations' abilities to digest milk, the team sequenced three genomic regions thought to influence the activity of the lactase-encoding LCT gene in 819 Africans from 63 different populations and 154 non-Africans from nine different populations in Europe, the Middle East and Central and East Asia.

They also examined the results of the lactose tolerance test in 513 people from 50 populations in East Africa.

Their sequencing and phenotyping efforts confirmed the association between lactase persistence and three known single-nucleotide polymorphisms, or SNPs, places where the DNA sequence varies in just one "letter." But they also identified two new SNPs associated with the trait located in regions that are thought to regulate lactase gene expression.

Their analysis revealed strong evidence of recent positive selection affecting several variants associated with lactase persistence in African populations, likely in response to the cultural development of pastoralism. The distinct geographic patterns in which these variants were present correlate in many cases with historic human migrations, mixing between populations as well as the spread of cattle, camels or sheep.

For example, they found the variant associated with lactase persistence in Europeans, T-13910, in central and northern African pastoralist groups, suggesting that these groups may have mixed historically with a non-African population.

The age of this genetic mutation is estimated to be 5,000-12,300 years old, coinciding with the origins of cattle domestication in North Africa and the Middle East. And a variant, G-13915, found at high frequencies in the Arabian Peninsula, and also present in northern Kenya and northern Sudan, dates to roughly 5,000 years ago, around the time that archaeological evidence suggests that camels were domesticated in the region.

Another variant, G-13907, was identified in the northern reaches of Sudan and Kenya as well as in Ethiopia. The researchers speculate that the mutation may have arisen in Cushitic populations in Ethiopia, who later migrated into Kenya and Sudan in the last 5,000 years.

They observed still another variant, C-14010, in Tanzania and Kenya as well as in southern Africa. This variant is believed to have arisen 3,000 to 7,000 years ago, a timing in line with the migration of pastoralists from North Africa into East Africa. The researchers' analysis suggests that this variant spread more recently into southern African, perhaps only in the last 1,000 years.

"We're starting to paint a picture of convergent evolution," Tishkoff said. "Our results are showing different mutations arising in different places that are under selection and rising to high frequencies and then reintroduced by migration to new areas and new populations."

Even with the new variants the Penn team identified, there were still patterns that the genetic data couldn't explain. Some groups that appeared to be able to digest milk lacked any genetic sign of this ability. The Hadza, nearly half of whom had the lactase persistence trait, are one example.

"This raises the strong possibility that there are other variants out there, perhaps in regions of the genome we haven't yet examined," Tishkoff said.

Another possibility is that commensal bacteria in the gut could offer humans a helping hand in digesting milk. The team is now assaying Africans' gut bacteria to see if that might be the case.

Additional co-authors on the study included Michael C. Campbell, Jibril B. Hirbo and Wen-Ya Ko of Penn's Department of Genetics; Alain Froment of the Musee de l'Homme in Paris; Paolo Anagnostou of Universita' La Sapienza and Istituto Italiano di Antropologia in Rome; Maritha J. Kotze of the University of Stellenbosch in South Africa; Muntaser Ibrahim of the University of Khartoum; Thomas Nyambo of Muhimbili University of Health and Allied Sciences in Tanzania; and Sabah A. Omar of the Kenya Medical Research Institute.

.


Related Links
University of Pennsylvania
Farming Today - Suppliers and Technology






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





FARM NEWS
Success of new bug-fighting approach may vary from field to field
Champaign IL (SPX) Mar 16, 2014
A new technique to fight crop insect pests may affect different insect populations differently, researchers report. They analyzed RNA interference (RNAi), a method that uses genetic material to "silence" specific genes - in this case genes known to give insect pests an advantage. The researchers found that western corn rootworm beetles that are already resistant to crop rotation are in some case ... read more


FARM NEWS
Millions join satellite search for missing plane

Ground Validation: Contributing to Earth Observations from Space

European Parliament adopts earth observation programme Copernicus

China satellite finds 'suspected crash site' in Malaysia jet hunt

FARM NEWS
ESA to certify first Galileo position fixes worldwide

Russia plans to launch new Glonass satellite on March 24

McMurdo Announces Global Availability of Maritime Fleet Management Software

Fifth Boeing GPS IIF Spacecraft Sends Initial Signals from Space

FARM NEWS
Amazon Inhales More Carbon than It Emits

Indonesian president intervenes in roaring forest blaze

Light pollution impairs rainforest regeneration

Agroforestry can ensure food security and mitigate the effects of climate change in Africa

FARM NEWS
Renewable chemical ready for biofuels scale-up

Maverick and PPE To Make Small-scale Methane-to-Methanol Plants

Boeing, South African Airways Explore Ways for Farmers to Grow More Sustainable Biofuel Crops

MSU advances algae's viability as a biofuel

FARM NEWS
Research Partnership With Cutting Edge 24/7 Solar Technology

Next-Gen PV Technologies to Take Center Stage as Solar Expenditures Rebound

Sale of Bosch Solar Energy's cell and module production in Arnstadt to SolarWorld

California Firm Awarded Patent for Zero-Fuel Solar Plastic Molding Technology

FARM NEWS
A new algorithm improves the efficiency of small wind turbines

Taming hurricanes

Wind farms can tame hurricanes: scientists

Draft report finds no reliable link between wind farms and health effects

FARM NEWS
Your money or your life: coal miner's dilemma mirrors China's

Societal Benefits of Fossil Energy to be at Least 50 Times Greater than Perceived Costs of Carbon

Goldman Sachs pulls out from Pacific coal export project

Colombia stops Drummond coal shipments over environmental row

FARM NEWS
UN experts condemn death of Chinese dissident

China denies mistreating dead dissident

China detains rebel village official: Xinhua

China attacker stabs five to death after row: police




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.