Featured Research

from universities, journals, and other organizations

Digesting milk in Ethiopia: A case of multiple genetic adaptations

Date:
August 29, 2013
Source:
University College London
Summary:
A genetic phenomenon that allows for the selection of multiple genetic mutations that all lead to a similar outcome -- for instance the ability to digest milk -- has been characterized for the first time in humans.

A genetic phenomenon that allows for the selection of multiple genetic mutations that all lead to a similar outcome -- for instance the ability to digest milk -- has been characterised for the first time in humans.
Credit: © volff / Fotolia

A genetic phenomenon that allows for the selection of multiple genetic mutations that all lead to a similar outcome -- for instance the ability to digest milk -- has been characterised for the first time in humans.

Related Articles


The phenomenon, known as a 'soft selective sweep', was described in the population of Ethiopia and reveals that individuals from the Eastern African population have adapted to be able to digest milk, but via different mutations in their genetic material.

A team of geneticists from UCL, University of Addis Ababa and Roskilde University have shown that five different alleles are found in the Ethiopian population that cause adult lactase production, one of which is newly confirmed. Their study is published in The American Journal of Human Genetics.

Professor Dallas Swallow, from the Department of Genetics, Evolution and Environment, senior author of the paper said: "Our genetic make-up determines our ability to digest milk into adulthood. Just over a third of the global population have inherited genes that allow us to make lactase, the enzyme that digests milk, as adults.

"This study shows that several different genetic changes that allow our bodies to make lactase have emerged independently. Changes to our lifestyle over the past 10,000 years -- including diet, altitude acclimatisation and infectious disease resistance -- will likely have caused many genetic adaptations of this kind."

We need lactase when we are babies to digest our mother's milk, so in babies large amounts of lactase enzyme are expressed by our genes. When we are older we no longer rely on our mother's milk for essential nutrients, so in most humans manufacture of the lactase enzyme stops through de-activation of the corresponding gene.

However, subtle mutations in the regulatory region of the gene in some individuals cause lactase to carry on being expressed into adulthood. Different mutations are likely to affect lactase expression using slightly different mechanisms. This parallel selection of different gene mutations that have the same phenotypic effect -- in this case lactase persistence -- is known as a soft selective sweep.

Soft selective sweeps have not been so clearly described before in humans, one reason being that variations caused by soft selective sweeps are more likely to be caused by genetic mutations in regulatory sequences, rather than mutations found in coding regions of genes.

Most statistical methods that analyse genetic variation assume we are looking for only one variation as the cause of genetic adaptation. But, in soft selective sweep patterns, more than one genetic variation is selected in parallel, which makes them more difficult to detect.

Dr Bryony Jones, also from the UCL Department of Genetics, Evolution and Environment, and lead author of the paper said: "Such variations have so far been very poorly studied and it will be important for them to be better characterised to understand better the relationship between historic adaptation and 21st century disease susceptibility."

Only in the last 5-10,000 years have humans started drinking the milk of other animals, following advances in our ability to herd animals. In times of plenty, being able to drink the milk of other animals would not have given a particular advantage to those with lactase persistence.

However, in situations where food sources became scarce, individuals capable of producing lactase as adults would be able to drink the milk of their animals, increasing their chances of survival.

Ethiopia has been subject to frequent droughts that contribute to famine. Individuals who can digest milk are more likely to increase their chance of survival under these conditions.

Dr Jones explained: "Ethiopia has been a cross-roads of human migrations in the last five thousand years since the lactase persistence genes are likely to have come under selection.

"Our studies on other African and Middle Eastern populations show quite different geographic distributions, with overlap in Ethiopia, suggesting that their origins are all different, but determining where these were and how they spread is likely to be difficult."

Professor Swallow said: "The combination of mutation, large effective population size, migration and selection has been shown to be important in generating this kind of pattern of diversity, namely parallel selection of multiple alleles of similar function, a so-called soft selective sweep."


Story Source:

The above story is based on materials provided by University College London. Note: Materials may be edited for content and length.


Journal Reference:

  1. Bryony L. Jones, Tamiru O. Raga, Anke Liebert, Pawel Zmarz, Endashaw Bekele, E. Thomas Danielsen, Anders Krüger Olsen, Neil Bradman, Jesper T. Troelsen, Dallas M. Swallow. Diversity of Lactase Persistence Alleles in Ethiopia: Signature of a Soft Selective Sweep. The American Journal of Human Genetics, 2013; DOI: 10.1016/j.ajhg.2013.07.008

Cite This Page:

University College London. "Digesting milk in Ethiopia: A case of multiple genetic adaptations." ScienceDaily. ScienceDaily, 29 August 2013. <www.sciencedaily.com/releases/2013/08/130829124345.htm>.
University College London. (2013, August 29). Digesting milk in Ethiopia: A case of multiple genetic adaptations. ScienceDaily. Retrieved December 20, 2014 from www.sciencedaily.com/releases/2013/08/130829124345.htm
University College London. "Digesting milk in Ethiopia: A case of multiple genetic adaptations." ScienceDaily. www.sciencedaily.com/releases/2013/08/130829124345.htm (accessed December 20, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Saturday, December 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Researchers Test Colombian Village With High Alzheimer's Rates

Researchers Test Colombian Village With High Alzheimer's Rates

AFP (Dec. 19, 2014) — In Yarumal, a village in N. Colombia, Alzheimer's has ravaged a disproportionately large number of families. A genetic "curse" that may pave the way for research on how to treat the disease that claims a new victim every four seconds. Duration: 02:42 Video provided by AFP
Powered by NewsLook.com
Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Reuters - Light News Video Online (Dec. 19, 2014) — Millions of monarch butterflies begin to descend onto Mexico as part of their annual migration south. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com
The Best Protein-Filled Foods to Energize You for the New Year

The Best Protein-Filled Foods to Energize You for the New Year

Buzz60 (Dec. 19, 2014) — The new year is coming and nothing will energize you more for 2015 than protein-filled foods. Fitness and nutrition expert John Basedow (@JohnBasedow) gives his favorite high protein foods that will help you build muscle, lose fat and have endless energy. Video provided by Buzz60
Powered by NewsLook.com
Birds Might Be Better Meteorologists Than Us

Birds Might Be Better Meteorologists Than Us

Newsy (Dec. 19, 2014) — A new study suggests a certain type of bird was able to sense a tornado outbreak that moved through the U.S. a day before it hit. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins