Continuing news of epigenetics:
Information about epigenetic markers continues apace. (Robert. J. Schmitz The Secret Garden – Epigenetic Alleles Underlie Complex Traits SCIENCE vol. 343 no. 6175 March 7, 2014 page 1082 and Sandra Cortijo et al. Mapping the Epigenetic Basis of Complex Traits page 1145 in the same issue.
Some traits, such as blood type, are inherited as single genes or as simple combinations. Some, such as height, are inherited as combinations of many genes; these are the complex traits. Things (that are not themselves genes) that affect the expression of genes are epigenetic. There are multiple mechanisms, the most widely discussed being adding methyl groups to genes without altering the DNA sequence. You will remember that it was found that stripping methyl groups off the plant Arabidopsis thaliana removed all inbreeding depression. Well the same plant has now been used in further study of methylation effects.
Plants have more inherited methylation effect than animals. Of course our major interest is in animals, but what has been learned is that it is possible to map methylation patterns, follow them from generation to generation and map out what epigenetic markers are having what effects; and at least some of those effects are upon complex traits.
I think nobody would doubt that fertility in humans is a complex trait. It is certainly a complex social process in the urbanified world. But so far the interest remains, “What effect does this methylation pattern have on its host gene?” They haven’t got around to asking, “What effect does this pattern of methylation on this gene have when matched or not matched with the methylation pattern on the homologous gene on the homologous chromosome?”
Some day, perhaps.
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