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regions, over 200 of the 3600 selected genes were differentially methylated
in parents, and more than 800 in the offspring. Among genes carrying
differential methylation, 79% were hypermethylated in White Leghorns, indi-
cating that this breed has accumulated methylations during domestication.
This suggests that selection for favorable epigenetic variation may have been
an important aspect of domestication.
A particularly interesting aspect of the experiment is the fact that differen-
tial gene expression profiles, as well as methylation differences, were reliably
inherited by the offspring, so there was high transgenerational stability in the
epigenetic effects. This further supports the importance of epigenetic selection
as a driver of phenotypic changes during domestication. The last piece of
evidence along this line from the same study is the observation that differen-
tially methylated loci were significantly more common in previously identified
selective sweep regions associated with domestication of layer breeds. This
strongly suggests that a significant proportion of the observed differential
methylations may have been subject to directed selection.
CLOSING REMARKS
We are in the middle of one of the most dynamic developmental phases in
biology ever experienced. Full-genome sequencing is becoming faster and
cheaper every year, and epigenetic screening is developing at an unprecedented
rate. Hence, we can foresee a rapid increase in knowledge regarding how
genetic variation is related to phenotypic differences. This will of course also be
the case for animal behavior.
The challenge faced by scientists will be to provide reliable phenotypic mea-
surements. Among all possible phenotypes, behavior stands out as particularly
difficult. It is the first and fastest way in which an animal will react to any stimu-
lus, and will therefore vary with almost any environmental factor (unlike, for
example, color or size). The obvious solution to this is to standardize behavioral
tests as much as possible, and this introduces the risk of distancing the recordings
more and more from natural conditions. This is a highly sensitive balance, and
it will take a high degree of scientific skill from the researchers of the future.
The ultimate goal of the research will be to find the causative genetic poly-
morphisms responsible for the domesticated behavior. This will be of enormous
importance to anyone interested in the biology and welfare of domesticated
animals, but equally so for those mainly concerned with the mechanisms of
evolution.
REFERENCES
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