Page 80 - CB1.3 Genetic Varation sciPAD

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80 CB 1.3 GENETIC VARIATION
USING KNOWLEDGE OF GENETICS
Using DNA to Trace Origins
The first scientist to think of using differences in our DNA to trace our
origins and relatedness grew up on a farm in Pukekohe.
Allan Wilson (1934-1991) led a group of evolutionary biologists
who realised that we could reconstruct human history by studying
markers in our mitochondrial DNA (mtDNA).
When DNA is passed from one generation to the next, most of it is
mixed by the processes that make each person unique from his or
her parents.
Some special types of DNA, however, remain virtually unaltered as
they pass from parent to child. One of these types is called ‘mitochondrial
DNA’ (mtDNA), which is inherited entirely from the mother, and not mixed up
with the father’s DNA during fertilisation.
Approximately once every 100 generations, a mutation occurs in this mtDNA. Once a mutation
occurs, it is passed on to all future generations of that woman’s children - it becomes an inheritable
genetic marker.
After several generations, a particular genetic marker is carried by almost all inhabitants of the
region in which it arose. When people leave that region, they carry the marker with them. By
studying the genes of many different indigenous populations, scientists can trace when and
where a particular marker arose. Each marker contained in a person’s DNA represents a location
and migration pattern of that person’s ancient ancestors.
These figures represent an ancestral
population. Each figure is a female.
Occasionally there is a mutation on the
mtDNA. This mutation is passed down to
the next generation.
The mutations in the mtDNA happen at
a fairly constant rate over time, so by
counting the number of differences in
the DNA between two different people,
scientists can work out how much time
has passed since those people diverged
from a common ancestor. The more
differences between two people, the
less closely related they are likely to be.
Some lineages die out over time.
1. Describe the key difference between ‘DNA’ and ‘mtDNA’ in terms of inheritance.




Tracing Whakapapa
Māori oral history describes how their tūpuna arrived in New Zealand as the result of the voyage
of a large number of waka from an island called Hawaiki. Hawaiki is a place of great importance
in Māori tradition, and appears in many songs and proverbs. The exact location of Hawaiki is
unknown.
Although it was once believed that the ancestors of Māori came to New Zealand in a single ‘great
fleet’ of seven waka, we now know that many waka made the perilous voyage. Through stories
passed down through the generations, modern Māori whakapapa to the captains and crews of
these ocean-going waka.
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