Anglojew
01-07-2014, 10:07 PM
Study focused on DNA differences across globe with the A111T mutation
Those who had mutation also shared traces of an ancestral genetic code
This indicates that all instances of mutation originate from same person
The mutated segment of DNA was itself created from a combination of two other mutations commonly found in East Asians
Light skin in Europeans stems from a gene mutation from a single person who lived 10,000 years ago.
This is according to a new U.S. study that claims the colour is due to an ancient ancestor who lived somewhere between the Middle East and the Indian subcontinent.
Scientists made the discovery after identifying a key gene that contributes to lighter skin colour in Europeans.
In earlier research, Keith Cheng from Penn State College of Medicine reported that one amino acid difference in the gene SLC24A5 is a key contributor to the skin colour difference between Europeans and West Africans.
‘The mutation in SLC24A5 changes just one building block in the protein, and contributes about a third of the visually striking differences in skin tone between peoples of African and European ancestry,’ he said.
He added the lighter skin colour may have provided an advantage due to the better creation of vitamin D from sunlight in the dark northern latitudes.
Building on this research, Professor Victor Canfield worked with Professor Cheng to study DNA sequence differences across the globe.
They studied segments of genetic code that have a mutation and are located closely on the same chromosome and are often inherited together.
The a mutation, called A111T, is found in virtually every one of European ancestry.
A111T is also found in populations in the Middle East and Indian subcontinent, but not in high numbers in Africans.
Penn State College of Medicine's Keith Cheng identified a key gene that contributes to lighter skin colour in Europeans and differs from West Africans
They discovered that all individuals from the Middle East, North Africa, East Africa and South India who carry the A111T mutation share traces of the ancestral genetic code.
According to the researchers, this indicates that all existing instances of this mutation originate from the same person.
The pattern of people with this lighter skin colour mutation suggests that the A111T mutation occurred somewhere between the Middle East and the Indian subcontinent.
‘This means that Middle Easterners and South Indians, which includes most inhabitants of India, Pakistan and Bangladesh, share significant ancestry,’ Professor Cheng said.
This mutated segment of DNA was itself created from a combination of two other mutated segments commonly found in Eastern Asians - traditionally defined as Chinese, Japanese and Korean.
‘The coincidence of this interesting form of evidence of shared ancestry of East Asians with Europeans, within this tiny chromosomal region, is exciting,’ said Professor Cheng.
‘The combining of segments occurred after the ancestors of East Asians and Europeans split geographically more than 50,000 years ago; the A111T mutation occurred afterward.’
Professor Cheng now plans to look at more genetic samples to better understand what genes play the most important role in East Asian skin colour.
Newly released genomes from around a dozen early inhabitants of Europe suggest that the continent was once a melting pot in which brown-eyed farmers encountered blue-eyed hunter-gatherers.
A report in Nature claims that present-day Europeans have ancestry from three groups in various combinations:
Hunter-gatherers, some of them blue-eyed, who came from Africa more than 40,000 years ago
Middle Eastern farmers who migrated west much more recently
A mysterious population whose range may have spanned northern Europe and Siberia
These three groups were identified from the genomes of 8,000-year-old hunter-gatherers - one man from Luxembourg and seven individuals from Sweden - as well as the genome of a 7,500-year-old woman from Germany. The study was led by the University of Tübingen in Germany.
The research suggests that the individuals from Luxembourg and Spain probably had dark-skin and blue eyes. The German woman, meanwhile, had brown eyes and lighter skin, and was related to Middle Eastern groups.
Both the Luxembourg hunter-gatherer and the German farmer had a gene that breaks down saliva - and a feature that may have came about due to agricultural life.
However, neither of them had the ability to digest the sugar lactose, found in milk. The trait originally emerged in the Middle East after the domestication of cattle and later spread to Europe.
Previous studies suggested that Europeans today largely descended from Middle Eastern farmers.
Read more: http://www.dailymail.co.uk/sciencetech/article-2535288/Light-skin-colour-Europeans-stems-ONE-ancestor-lived-India-Middle-East-10-000-years-ago.html#ixzz2pkyFQNyL
-I personally am skeptical because a 2008 study stated the same thing about blue-eyes;
People with blue eyes have a single, common ancestor, according to new research.
A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes.
"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.
The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin.
"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.
The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.
"It's exactly what I sort of expected to see from what we know about selection around this area," said John Hawks of the University of Wisconsin-Madison, referring to the study results regarding the OCA2 gene. Hawks was not involved in the current study.
Baby blues
Eiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages.
They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production.
Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.
"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.
Melanin switch
The mutation is what regulates the OCA2 switch for melanin production. And depending on the amount of melanin in the iris, a person can end up with eye color ranging from brown to green. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.
"Out of 800 persons we have only found one person which didn't fit — but his eye color was blue with a single brown spot," Eiberg told LiveScience, referring to the finding that blue-eyed individuals all had the same sequence of DNA linked with melanin production.
"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg said. "They have all inherited the same switch at exactly the same spot in their DNA." Eiberg and his colleagues detailed their study in the Jan. 3 online edition of the journal Human Genetics.
That genetic switch somehow spread throughout Europe and now other parts of the world.
"The question really is, 'Why did we go from having nobody on Earth with blue eyes 10,000 years ago to having 20 or 40 percent of Europeans having blue eyes now?" Hawks said. "This gene does something good for people. It makes them have more kids."
http://www.livescience.com/9578-common-ancestor-blue-eyes.html
However, this is contradicted now with claims Europe had a hunter-gatherer population with blue-eyes up to 40,000 years ago (eg in first article above).
Those who had mutation also shared traces of an ancestral genetic code
This indicates that all instances of mutation originate from same person
The mutated segment of DNA was itself created from a combination of two other mutations commonly found in East Asians
Light skin in Europeans stems from a gene mutation from a single person who lived 10,000 years ago.
This is according to a new U.S. study that claims the colour is due to an ancient ancestor who lived somewhere between the Middle East and the Indian subcontinent.
Scientists made the discovery after identifying a key gene that contributes to lighter skin colour in Europeans.
In earlier research, Keith Cheng from Penn State College of Medicine reported that one amino acid difference in the gene SLC24A5 is a key contributor to the skin colour difference between Europeans and West Africans.
‘The mutation in SLC24A5 changes just one building block in the protein, and contributes about a third of the visually striking differences in skin tone between peoples of African and European ancestry,’ he said.
He added the lighter skin colour may have provided an advantage due to the better creation of vitamin D from sunlight in the dark northern latitudes.
Building on this research, Professor Victor Canfield worked with Professor Cheng to study DNA sequence differences across the globe.
They studied segments of genetic code that have a mutation and are located closely on the same chromosome and are often inherited together.
The a mutation, called A111T, is found in virtually every one of European ancestry.
A111T is also found in populations in the Middle East and Indian subcontinent, but not in high numbers in Africans.
Penn State College of Medicine's Keith Cheng identified a key gene that contributes to lighter skin colour in Europeans and differs from West Africans
They discovered that all individuals from the Middle East, North Africa, East Africa and South India who carry the A111T mutation share traces of the ancestral genetic code.
According to the researchers, this indicates that all existing instances of this mutation originate from the same person.
The pattern of people with this lighter skin colour mutation suggests that the A111T mutation occurred somewhere between the Middle East and the Indian subcontinent.
‘This means that Middle Easterners and South Indians, which includes most inhabitants of India, Pakistan and Bangladesh, share significant ancestry,’ Professor Cheng said.
This mutated segment of DNA was itself created from a combination of two other mutated segments commonly found in Eastern Asians - traditionally defined as Chinese, Japanese and Korean.
‘The coincidence of this interesting form of evidence of shared ancestry of East Asians with Europeans, within this tiny chromosomal region, is exciting,’ said Professor Cheng.
‘The combining of segments occurred after the ancestors of East Asians and Europeans split geographically more than 50,000 years ago; the A111T mutation occurred afterward.’
Professor Cheng now plans to look at more genetic samples to better understand what genes play the most important role in East Asian skin colour.
Newly released genomes from around a dozen early inhabitants of Europe suggest that the continent was once a melting pot in which brown-eyed farmers encountered blue-eyed hunter-gatherers.
A report in Nature claims that present-day Europeans have ancestry from three groups in various combinations:
Hunter-gatherers, some of them blue-eyed, who came from Africa more than 40,000 years ago
Middle Eastern farmers who migrated west much more recently
A mysterious population whose range may have spanned northern Europe and Siberia
These three groups were identified from the genomes of 8,000-year-old hunter-gatherers - one man from Luxembourg and seven individuals from Sweden - as well as the genome of a 7,500-year-old woman from Germany. The study was led by the University of Tübingen in Germany.
The research suggests that the individuals from Luxembourg and Spain probably had dark-skin and blue eyes. The German woman, meanwhile, had brown eyes and lighter skin, and was related to Middle Eastern groups.
Both the Luxembourg hunter-gatherer and the German farmer had a gene that breaks down saliva - and a feature that may have came about due to agricultural life.
However, neither of them had the ability to digest the sugar lactose, found in milk. The trait originally emerged in the Middle East after the domestication of cattle and later spread to Europe.
Previous studies suggested that Europeans today largely descended from Middle Eastern farmers.
Read more: http://www.dailymail.co.uk/sciencetech/article-2535288/Light-skin-colour-Europeans-stems-ONE-ancestor-lived-India-Middle-East-10-000-years-ago.html#ixzz2pkyFQNyL
-I personally am skeptical because a 2008 study stated the same thing about blue-eyes;
People with blue eyes have a single, common ancestor, according to new research.
A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes.
"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.
The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin.
"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.
The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.
"It's exactly what I sort of expected to see from what we know about selection around this area," said John Hawks of the University of Wisconsin-Madison, referring to the study results regarding the OCA2 gene. Hawks was not involved in the current study.
Baby blues
Eiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages.
They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production.
Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.
"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.
Melanin switch
The mutation is what regulates the OCA2 switch for melanin production. And depending on the amount of melanin in the iris, a person can end up with eye color ranging from brown to green. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.
"Out of 800 persons we have only found one person which didn't fit — but his eye color was blue with a single brown spot," Eiberg told LiveScience, referring to the finding that blue-eyed individuals all had the same sequence of DNA linked with melanin production.
"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg said. "They have all inherited the same switch at exactly the same spot in their DNA." Eiberg and his colleagues detailed their study in the Jan. 3 online edition of the journal Human Genetics.
That genetic switch somehow spread throughout Europe and now other parts of the world.
"The question really is, 'Why did we go from having nobody on Earth with blue eyes 10,000 years ago to having 20 or 40 percent of Europeans having blue eyes now?" Hawks said. "This gene does something good for people. It makes them have more kids."
http://www.livescience.com/9578-common-ancestor-blue-eyes.html
However, this is contradicted now with claims Europe had a hunter-gatherer population with blue-eyes up to 40,000 years ago (eg in first article above).