Dr Mrazek told BBC News Online that it was possible that the stress associated with parental problems caused chemical changes in the body that had an effect on the function of genes thought to be linked to the development of asthma.

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This vast majority of genetic material known as functional noncoding DNA, mostly embedded within and around the genes, was thought to play an important but murky role in regulating how the coding genes go about their business.

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Many diseases of old age, such as Alzheimer's, are now thought to be linked to changes in mitochondrial genes.

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And it means that in female cells a certain proportion of activated genes exist in higher concentrations than was once thought.

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Stefansson left his spot as a professor at Harvard Medical School to found DeCode because he thought his native Iceland provided the perfect spot for discovering genes in families with lineages that have been tracked for generations.

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It was thought that having these mutations, to the BRCA1 and BRCA2 genes, could make healthy cells less able to repair any damage caused by radiotherapy.

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This was thought to ensure that their offspring have as wide a range of immune response genes - and therefore greater protection against infection - as possible.

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Scientists once thought of that stuff as junk, but many now believe it may regulate how the genes work or provide some other function.

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