January 24, 2007

Sub-Saharan African Y chromosome haplogroup A in white British surname

From the BBC story:
People of African origin have lived in Britain for centuries, according to genetic evidence.

A Leicester University study found that seven men with a rare Yorkshire surname carry a genetic signature previously found only in people of African origin.

The men seem to have shared a common ancestor in the 18th Century, but the African DNA lineage they carry may have reached Britain centuries earlier.


By chance, the researchers discovered a white man with a rare Yorkshire surname carrying a Y chromosome haplogroup that had previously been found only in West African men. And even there, it is relatively uncommon.

"We found that he was in haplogroup A1, which is highly West African-specific," said Turi King, a co-author on the study at the University of Leicester.

"It is incredibly rare, there are only 25 other people known worldwide and they are all African."


Prior to the 20th Century, there have been various routes by which people of African ancestry might have reached Britain. For example, the Romans recruited from Africa and elsewhere for the garrison that guarded Hadrian's Wall.


Another major route was through the slave trade.

"Some of the Africans who arrived in Britain through the slave trade rose quite high up in society, and we know they married with the rest of the population," said Ms King.

"It could be either of these two routes," she said. Even if the two family trees link up in the 18th Century, haplogroup A1 could have reached Britain long before that.

"But my guess is that, because many slaves came from West Africa, it could have been through that route," Ms King told BBC News.
From the EurekAlert release:
New research has identified the first genetic evidence of Africans having lived amongst "indigenous" British people for centuries. Their descendants, living across the UK today, were unaware of their black ancestry.


"As you can imagine, we were pretty amazed to find this result in someone unaware of having any African roots," explains Professor Jobling, a Wellcome Trust Senior Research Fellow. "The Y chromosome is passed down from father to son, so this suggested that Mr. X must have had African ancestry somewhere down the line. Our study suggests that this must have happened some time ago."

Although most of Britain's one million people who define themselves as "Black or Black British" owe their origins to immigration from the Caribbean and Africa from the mid-twentieth century onwards, in reality, there has been a long history of contact with Africa. Africans were first recorded in the north 1800 years ago, as Roman soldiers defending Hadrian's Wall.

To investigate the origins of hgA1 in Britain, the team recruited and studied a further eighteen males with the same surname as Mr. X. All but one were from the UK, with paternal parents and grandparents also born in Britain. Six, including one male in the US whose ancestors had migrated from England in 1894, were found to have the hgA1 chromosome.


"This study shows that what it means to be British is complicated and always has been," says Professor Jobling. "Human migration history is clearly very complex, particularly for an island nation such as ours, and this study further debunks the idea that there are simple and distinct populations or 'races'." [DP: This is a common fallacious argument against the existence of biological races; demand that races be completely genetically distinct, and then "debunk" their existence at any slightest sign of intermixture. It is indeed the distinctness of the European and Sub-Saharan African Y chromosome pools that allows us to infer the origin of rare outliers. Human races are not isolated islands, but rather more or less sharply defined hills or mountains on the genetic landscape].

In addition, Professor Jobling believes that the research may have implications for DNA profiling in criminal investigations.

"Forensic scientists use DNA analysis to predict a person's ethnic origins, for example from hair or blood samples found at a crime scene. Whilst they are very likely to predict the correct ethnicity by using wider analysis of DNA other than the Y chromosome, finding this remarkable African chromosome would certainly have them scratching their heads for a while."
I don't see the EJHG article on the website yet, feel free to leave a comment if I missed it or it is published online.

[UPDATE] From the paper:
Our study shows that a globally rare Y-chromosome type, belonging to the deepest-rooting African branch of the Y-phylogeny, has been present in Northern England since at least the mid-18th century. HgE3a is by far the most frequent Y-chromosomal lineage in Africa, existing at 48% in a continent-wide sample of 1122 chromosomes,30 so we would expect any substantial past immigration from Africa to Britain to have left examples of chromosomes belonging to this common hg. However, a survey of 1772 Y chromosomes from the British Isles found none,13 and they are also absent from our control sample of 421 chromosomes. The general rarity of African lineages may reflect a low level of initial introgression, later loss through drift, or sampling bias – for example, the large British survey13 sampled from small towns, in which the descendants of early British Africans, who were concentrated in cities, may be depleted.

Admixture between populations of African and European origin is often sex-biased, with a greater proportion of the African component of the hybrid population being contributed by females.48 Assuming an equal number of males and females of African origin migrating to Britain, we might therefore expect mitochondrial DNA to reveal a stronger signal of African admixture than the Y chromosome. There is little published evidence, but a study of mitochondrial DNA sequence diversity among 100 'white Caucasian' British49 does contain one haplotype, which represents an hg L1c sequence (defined according to Salas et al.50), with a probable origin in West Central Africa.51 This could represent a possible maternal counterpart to the Y-lineage we describe here.

Here is the abstract:

European Journal of Human Genetics (advance online publication)

Africans in Yorkshire? The deepest-rooting clade of the Y phylogeny within an English genealogy

Turi E King et al.


The presence of Africans in Britain has been recorded since Roman times, but has left no apparent genetic trace among modern inhabitants. Y chromosomes belonging to the deepest-rooting clade of the Y phylogeny, haplogroup (hg) A, are regarded as African-specific, and no examples have been reported from Britain or elsewhere in Western Europe. We describe the presence of an hgA1 chromosome in an indigenous British male; comparison with African examples suggests a Western African origin. Seven out of 18 men carrying the same rare east-Yorkshire surname as the original male also carry hgA1 chromosomes, and documentary research resolves them into two genealogies with most-recent-common-ancestors living in Yorkshire in the late 18th century. Analysis using 77 Y-short tandem repeats (STRs) is consistent with coalescence a few generations earlier. Our findings represent the first genetic evidence of Africans among 'indigenous' British, and emphasize the complexity of human migration history as well as the pitfalls of assigning geographical origin from Y-chromosomal haplotypes.


No comments: