Question about DNA haplotype testing

Discussion in 'Biology & Genetics' started by At World's End, Mar 4, 2009.

  1. At World's End Registered Member

    Messages:
    79
    How can it be that ALL people who share a certain mutation in their DNA are assumed to have descended from ONE person who initially acquired the mutation? After all, aren't those DNA mutations supposed to be RANDOM? Can't two or more people who lived in different times and different places INDEPENDENTLY acquire the same mutation? Is the assumption wrong? Anyway, here's the stuff (sorry it's a bit long):

    "The marker M9 first appeared in a man born around 40,000 years ago in present day Iran or south-central Asia. This marked a new lineage diverging from the M89 Middle Eastern clan. His descendants spent the next 30,000 years populating much of the planet.

    This large lineage, called the Eurasian Clan, dispersed gradually over thousands of years. Seasoned hunters followed the herds ever eastward, along the vast 'highway' of the Eurasian Steppe. Eventually their path was blocked by the massive mountain ranges of south-central Asia: the Hindu Kush, the Tian Shan and the Himalayas. These three mountain ranges meet in the center of a region known as the Pamir Knot, located in present-day Tajikistan. Here the tribes of hunters split into two main groups. Some moved north into central Asia, others moved south into what is now Pakistan and the Indian subcontinent. These different migration routes through the Pamir Knot region gave rise to separate lineages. Most people of the Northern Hemisphere trace their roots to the Eurasian Clan. Nearly all North Americans and East Asians are descended from this man, as are most Europeans and many Indians."

    http://www.kknfa.org/haplogroups.htm
     
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  3. S.A.M. uniquely dreadful Valued Senior Member

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    72,825
    Not all mutations are equal. You need a frequency >1% in a population to classify as a SNP. You need a set of similar haplotypes derived from the SNP to form a haplogroup. You need a haplogroup to draw a map of migration.

    And there is usually more than one haplogroup in common.
     
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  5. iceaura Valued Senior Member

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    30,994
    It's a statistical likelihood. There weren't that many people involved, at the time, so two identical mutations at about the same time at a rare spot (we know it's rare because whole groups of billions of people apparently do not feature it) seem unlikely.

    If, say, the people populating the north had included a sizable number without the mutation, and then another man had mutated some time along the way (more recently) then there should be pockets of people without the mutation.
     
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