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SignOnSanDiego.com > News > Science -- Long in the tooth: "Mother lode
To follow this conversation for long you need a vocabulary word: mitochondrial DNA.
Most people are familiar with nuclear DNA � our genes that come to us courtesy of our mother and father, when the sperm fertilizes the egg and both sets of genes mix.
As a tool for genetic anthropologists, nuclear DNA is troublesome because all that reshuffling of genes makes it tough to trace a direct genetic line from individual to individual.
But the mitochondria, the cell's energy-producing bodies, also have tiny genomes, and these are inherited only from our mothers. Because there is no mixing with male genes, Smith explains, mitochondrial DNA stays the same from generation to generation, except when random mutations occur.
And mitochondrial DNA is abundant in cells compared to nuclear DNA and therefore more likely to be extracted. It will never be enough to clone an early cave man, but for Kemp, Smith and other genetic anthropologists, mitochondrial DNA is the mother lode.
'This is what's allowing us to construct a history where there is no written record,' Smith says.
The reason they can do this is because the rate of mutation in mitochondrial DNA remains constant over time � in each individual, from prehistory to modern-day, changes occur at the same rate. That rate of change is used as a measuring stick for time known as the molecular clock.
To make sense of all the mutations, scientists group individuals with similar sets of mutations into families known as haplogroups. Haplogroups are further divided into smaller groups called haplotypes. OYKCM belongs to haplotype D, one of five founding lineages that appear in North America. But his haplotype is rare.
'When I first saw it, I wasn't sure what I was looking at,"
To follow this conversation for long you need a vocabulary word: mitochondrial DNA.
Most people are familiar with nuclear DNA � our genes that come to us courtesy of our mother and father, when the sperm fertilizes the egg and both sets of genes mix.
As a tool for genetic anthropologists, nuclear DNA is troublesome because all that reshuffling of genes makes it tough to trace a direct genetic line from individual to individual.
But the mitochondria, the cell's energy-producing bodies, also have tiny genomes, and these are inherited only from our mothers. Because there is no mixing with male genes, Smith explains, mitochondrial DNA stays the same from generation to generation, except when random mutations occur.
And mitochondrial DNA is abundant in cells compared to nuclear DNA and therefore more likely to be extracted. It will never be enough to clone an early cave man, but for Kemp, Smith and other genetic anthropologists, mitochondrial DNA is the mother lode.
'This is what's allowing us to construct a history where there is no written record,' Smith says.
The reason they can do this is because the rate of mutation in mitochondrial DNA remains constant over time � in each individual, from prehistory to modern-day, changes occur at the same rate. That rate of change is used as a measuring stick for time known as the molecular clock.
To make sense of all the mutations, scientists group individuals with similar sets of mutations into families known as haplogroups. Haplogroups are further divided into smaller groups called haplotypes. OYKCM belongs to haplotype D, one of five founding lineages that appear in North America. But his haplotype is rare.
'When I first saw it, I wasn't sure what I was looking at,"
posted by Helen Campbell @ 9:39 PM
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