Monday, December 21, 2009

Gene effects differ depending on which parent they come from

In Iceland, they have a more-or-less complete genealogy and medical history on everybody in the country. It is funded by a private company, but Icelanders have bought into it. Some researchers recently used this database to look at particular gene alleles and their relation to diseases.

An article on the research in the New York Times discusses the genetic imprinting it found, which means that some genes have different effects on the body depending on whether they come from the mother or father. One gene variant increases the risk of Type 2 diabetes by 30% if it comes from the father, but it decreases the risk by 10% if it comes from the mother. Since they nearly cancel out, the importance of the gene had been overlooked when not taking into account which parent the allele came from.

The authors speculate that other genes might have opposite effects depending on which parent they come from and that this might explain why analyses that did not take this into account failed to find the genetic effects. Sounds plausible.

The whole idea of genetic imprinting is bizarre to me, but is well established. The obvious question is what evolutionary problem it solved. From wikipedia:
A widely accepted hypothesis for the evolution of genomic imprinting is the "parental conflict hypothesis." This hypothesis states that the inequality between parental genomes due to imprinting is a result of the differing interests of each parent in terms of the evolutionary fitness of their genes. The father is often more 'interested' in the growth of his offspring, at the expense of the mother. The mother's interest is often to conserve resources for her own survival while providing sufficient nourishment to current and subsequent litters.
Accordingly, paternally expressed genes tend to be growth promoting whereas maternally expressed genes tend to be growth limiting. In support of this hypothesis, genomic imprinting has been found in all placental mammals, where post-fertilization offspring resource consumption at the expense of the mother is high; it has not been found in oviparous birds or monotremes (a class of oviparous mammals) where there is relatively little post-fertilization resource transfer and therefore less parental conflict.

However, our understanding of the molecular mechanisms behind genomic imprinting show that it is the maternal genome that controls much of the imprinting of both its own and the paternally-derived genes in the zygote, making it difficult to explain why the maternal genes would willingly relinquish their dominance to that of the paternally-derived genes in light of the conflict hypothesis. Several other hypotheses that propose a coadaptive reason for the evolution of genomic imprinting have been proposed.

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