Epigenetics Connects the Genome to Its Environment - Plant Breeding Reviews - page 74

and sometimes, at least to some degree, passed on transgenerationally.
Any role of the environment in directing phenotype changes in evolu-
tion therefore has remained highly controversial. With the understand-
ing of random spontaneity of mutations (Muller 1930) and the dismissal
of an occasional passage of a clear environment-induced trait through
generations (Cullis 1981, 2005), a consensus formed that firmly estab-

lished the passive filtering role of the environment in any genome

changes (mutations). Eventually, environmental effects on phenotype
became viewed as noise and led to the establishment of population
genetics and statistical approaches toward genetic analysis (Pearson
1900; Gartner 1990; Finch and Kirkwood 2000) that have now reached
very sophisticated levels with the use of computer models and algo-
rithms (Hucka et al. 2003; Wilkinson 2006; Rand 2008).
Following the immense amount of work during the 20th century,
discrete sequences of DNA as the units of Mendelian inheritance were
established. The Central Dogma of information flow fromDNA to RNA to

proteins became accepted as the mechanism by which DNA sequences
were interpreted and controlled the phenotype, but this process was
considered not to be involved in directing informational changes that
affect transgenerational inheritance. At this point, the role of the envi-
ronment in natural (passive) selection was well established without any
serious challenge and evolution was increasingly seen in the form of the
Neo-Darwinian view or the Modern Synthesis Theory of Evolution
(MST) of Mayer and Huxley, a term that we use here to describe the
almost exclusive emphasis on DNA sequence of genes as the exclusive
focus of natural selection.
The only

still seemed to be how the same DNA
sequence that natural selection acted on was also somehow used by the
Central Dogma to manifest phenotype including cell specialization
during development. These unknown mechanisms were thought to
act so independently, that no changes in traits that are acquired during
development should be inherited. By this process of ontogeny, cells
change their phenotype from egg or stem cell to heart, liver, root, leaf,
and so on and organize themselves into tissues, organs, and eventually
the mature organism whose precise form results somehow from reading
the entire genome through the Central Dogma. We owe the concept of the
genome to the incredible chromosome transplant experiments per-
formed by Boveri (1904). Here he established that the ability of an
egg to form an adult organism required information present in total
on all of the chromosomes, our

“ “fly in the ointment ”

first hint of an integrated function of the

genome. Boveri must be passed from generation to

generation without being affected by the environment. In keeping with

' s entire “ genome ”