Inbreeding is a term used to describe the mating of two individuals with a similar genetical make-up. The offspring of such parents are generally born with certain detrimental traits. In case of the Habsburgs, the Austrian-Spanish royal family, marriages between close relatives for many generations led to destruction of the total bloodline (inbreeding depression). The offsprings of these genetically related parents were affected with recessive traits like infertility and mental illness.
For more than a century the scientific communities believed that these complications were caused by genetic mutations, that occurred when two genetically similar individuals bred. A recent study in plants shows that the reason for this inbreeding depression is not just the occurrence of a specific combination of genes, but the method in which these genes are switched on and off. The plant used for this study is Scabiosa columbaria, a native plant of Europe and Asia. This plant has dark green leaves and the flowers are tiny and delicate, purple in colour.
The credit for this discovery goes to Philippine Vergeer, a postdoc at the Radboud University, Netherlands. Vergeer observed that the inbred offsprings of this plant species showed a different kind of response to environmental conditions when compared to the outbred plants, which were not crossed with the close relatives. For example adverse conditions such as drought and unhealthy soil destroyed the inbred plants quicker.
Under adverse environmental conditions, the DNA of the plant undergoes epigenetic changes, which is the addition or removal of methyl groups that can turn the genes on or off. Vergeer was curious if these modifications were the cause of inbreeding depression. To confirm, Vergeer and colleagues took a count of methyl groups in the genomes of inbred and outbred plants. The inbred plants of S.columbaria had ten percent more methyl groups when compared to the outbred plants. This showed that the inbred plants had undergone epigenetic changes. The inbred plants were found to be unhealthy.
To show that methylation was the reason, scientists treated one batch of inbred S. columbaria with a demethylating agent called 5-azacytidine, which removes the methyl groups from DNA. The DNA methylation levels of these treated inbred plants roughly matched those of the outbred plants. The treated inbred plants were also healthy and registered a growth rate similar to the outbred plants.
The scientists do not have a clear picture on how epigenetics causes inbreeding depression. Vergeer contemplates that some of the rare genes that regulate the attachment and removal of methyl groups are exposed to inbreeding, causing abnormal methylation. Vergeer and colleagues aim to study the epigenetic effects in detail by finding out the specific genes that contain the methyl group and the point of attachment of these groups on the genes.
An evolutionary ecologist from the University of Bern, Switzerland, Oliver Bossdorf, says that this is the first study to expose the role of epigenetics in inbreeding depression. Bossdorf points that estimating epigenetics by counting the number of methyl groups is not a prompt measurement; Vergeer accepts this statement.
Vergeer says that these results can be beneficial to conservation biologists. Factors such as deforestation and human activities have disintegrated many species into small groups. The resulting inbreeding depression can cause extinction of the species. Vergeer points that the epigenetics will determine the inbred population’s response to environmental changes.
This study demonstrates the possibility to treat the destructive effects of inbreeding with 5-azacytidine or any related demthylating agent. This has to be analyzed.