Agriculture Reference
In-Depth Information
inheritance that is often transgenerational (Jablonka and Raz 2009) are
now being recognized. This recognition has
finally started to bring into
question the MST view championed by Huxley (1936, 1942) and Berry
and Bradshaw (1992). According to MST, the role of the environment in
evolution occurs only through natural selection based on the genotype.
Importantly, several in
uential work, especially of Gilbert Gottlieb at
the beginning of the Evolution of Development (Evo-Devo) Movement
in the 1980s (Jablonka 2007), began to emphasize that genetic inheri-
tance occurs through phenotype selection that is based on genotype
modules. This began to challenge the strictly speci
c gene inheritance
model of the MST that was rooted in Johanssen
s theories. When West-
Eberhard published her book
Developmental Plasticity and Evolution
,
the entire
'
field of biology began to reconsider the relationship of devel-
opment to genetics and evolution. Many of these very old ideas began to
resurface, and now can be appreciated greatly in the modern context of
epigenetics.
E. The Relationship of Genetics with Epigenetics: Resetting During
Development
Many traits that appear to be epigenetic in both plants and animals are
not only connected to growth but are also linked to responses to
hormonal signals that can exert powerful control over growth. For
instance, exposure of rat mothers and pups to a stressful environment
where the mother offers less care in the form of licking/grooming arched
back nursing (LG-ABN) causes an increased fear response in the pups
that persists into adulthood and is reversible by environment changes,
that is, epigenetic. The low LG-ABN trait has been traced to the effects of
the stressful environment on the gene expression of the nerve growth
factor inducible protein and its glucocorticoid receptor. This gene
expression change, although not proven to result from an epi change,
has been shown to be associated with promoter methylation status and
the associated histone acetylation pattern (Youngson and Whitelaw
2008).
The earlier and extensive work of Fred Meins and coworkers (Meins
et al. 1980; Meins and Foster 1986) has also linked a hormonally
controlled trait of plant cells and their growth to an apparent epigenetic
status. Although the epigenetic marks associated with cytokinin habitu-
ation of plant cells have never been identi
ed, Meins and coworkers
have shown that this trait is not only transgenerational but, remarkably,
its transgenerational inheritance also depends on the developmental
