Less than 50 people founded the entire population of Europe

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http://www.newscientist.com/dailynews/news.jsp?id=ns9999721

Less than 50 people founded the entire population of Europe, according to a new

and accurate way to read demographic

history from the genome.

Scientists previously believed that the 500 million people that live in Europe

today are ancestors of about 10,000

people who left Africa around 100,000 years ago.

But scientists from the Whitehead Institute at MIT in Cambridge, Massachusetts

have found so much genetic evidence of

inbreeding, they believe all Europeans probably descended from fewer than about

50 people who interbred together over

about 30 generations. This select group may have left Africa about 60,000 years

ago.

Their data comes from maps of single nucleotide polymorphisms (SNPs), which are

the single letter differences in DNA

which can exist between people.

The discovery is good news for medicine because the unexpectedly low degree of

genetic variation will make it far easier

to isolate the genes that underpin common diseases. " I'm very, very excited

about this, " said Lander of the

Whitehead Institute.

Chop and change

In every generation DNA sequences are shuffled by recombination, when genomes

from sperm and egg are chopped into chunks

and strung together. As one generation is followed by another, the repeated

shuffling means it is increasingly unlikely

that sets of SNPs will be shared by individuals.

Using this to date populations is far more accurate than the previous method of

measuring the mutation rate in

mitochondrial DNA, because recombination must occur in every generation whereas

mutation rates can vary.

From archaeological evidence, scientists expected to see SNPs correlated over

about 3000 base pairs. But Reich of

the Whitehead Institute found the genome was preserved in much larger chunks,

each about 160,000 base pairs long. This

points to a far more dramatic population bottleneck.

The average gene is about 30,000 base pairs long - much less than the number

over which SNPs correlate. Reich's

discovery therefore means it will be easier to find the genes that underpin

common diseases. This is because comparing

SNP maps from populations with and without the diseases will reveal the sections

which differ and these should contain

the suspect gene.

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Good Health & Long Life,

Greg ,

http://www.ozemail.com.au/~gowatson

gowatson@...