Monday, 16 July 2012

Inbreeding's Downside Is Not All in the Genes

The Habsburgs learned about inbreeding the hard way. Centuries of marriages between close relatives in this Austrian-Spanish royal family led to mental illness, infertility, and the eventual extinction of the entire bloodline. For more than a hundred years, scientists have chalked up such problems to rare genetic mutations, which come to the fore only when related individuals breed. But a new study in plants indicates that it's not just genes that lead to this so-called inbreeding depression; it's also how these genes are switched on and off.

Philippine Vergeer happened upon the discovery while working with the Scabiosa columbaria plant. Vergeer, currently a postdoc at Radboud University in Nijmegen, the Netherlands, noticed that inbred members of the species—which is native to Europe and Asia and has dark green leaves topped with small, delicate purple flowers—had very different responses to environmental conditions than plants that had not been crossed with close relatives. Drought and poor soil tended to kill the inbred plants quickly, for example, whereas the outbred plants were hardier.

Vergeer could have chalked it all up to harmful rare genes. But then she thought more about the environmental conditions. Drought and poor nutrition are known to cause so-called epigenetic changes to DNA, the addition or removal of small chemical tags known as methyl groups that effectively turn genes on or off. Could such modifications be causing inbreeding depression?

To find out, Vergeer and colleagues counted the methyl groups in the genomes of inbred and outbred S. columbaria. The inbred plants showed a variety of health problems, including difficulty photosynthesizing and slow maturation. They also had 10% more methyl groups in their genomes than did outbred plants, indicating significant epigenetic changes.