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Building a Reference Map

Using Population Profiles to Trace the Origin of Seized Ivory

Determining the origin of a particular ivory sample involves looking for shared alleles between the ivory and different elephant populations for each of the 16 genetic markers.

In this example, you can see the alleles for one of the markers in two elephant populations (A and B) and in the ivory sample. The ivory sample represents an individual elephant, so it only has two alleles for this marker. Populations A and B have many alleles. That’s because the population profiles are a composite of all alleles found in the individuals from each population.

Is the ivory sample more like population A or population B? The ivory sample has one allele of 243 bp that is present in both populations, and one allele of 236 bp that is only present in population A. Thus, based on just this marker, the ivory sample is more likely to have come from population A than B. By repeating this process for every allele and every population, also taking into account allele frequencies, scientists can determine the most likely population of origin.

In many cases, the ivory does not come from any of the populations from which DNA samples were obtained. By using a statistical model, scientists can trace the ivory to the most likely location between sampled populations.

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