Why aren’t DNA tests 100 per cent accurate?

Asked by: Gary Ward, US

Assuming there is enough DNA to read, DNA tests should certainly be able to identify genes – how you differ to other groups of people, say, if it were an ancestry test; or whether you have a gene variant associated with a predisposition to a disease.

But how that is understood, interpreted or used is where things get complicated. Many false-positive and false-negative results can happen because of ‘quirks’ in our chromosomes. You can get different estimates of how recently we share ancestors. And it’s hard to determine the significance of a mutation you may carry.

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