290 Raphael Falk
The new methods of DNA hybridization had no taxonomic inhibitions whatsoever,
and soon hybrid DNA molecules of, say mosquito, human and plant, were common
subjects for research. Genetic engineering, which allowed direct genetic compari-
son between any species and the transfer of genes from one species to individuals
of another, unrelated species, prompted the genetic analysis of the evolution of
developmental process, orevo-devo.
Molecular genetic analysis of homeotic mutants, in which one organ is trans-
formed into the likeness of another, usually a homologous one, revealed stretches
of DNA that were nearly identical in other genes with homeotic effects (like the
homeobox of some 180 nucleotides, that appear to be involved in when-and-where
particular groups of genes are expressed along the embryo axis during development
[McGinniset al., 1984a; McGinniset al., 1984b]). The method of determining ho-
mologies by comparing DNA sequences is nowadays done mainlyin silico.As
suggested many years ago [Ohno, 1970], the abundance of homologous sequences
in the same species genome (paralogous sequence that do not necessarily share
similar functions any more) or in different species (orthologous sequences that
‘usually’ have similar functions in different species), indicate that the system’s
structural and functional organization have been also causal factors rather than
merely consequences in the history of the process of evolution.
8 OPENING PANDORA’S BOX: CRACKS IN THE DOGMAIn 1946 Crick formulated the Central Dogma of Genetics:
I shall argue that the main function of the genetic material is to control
(not necessarily directly) the synthesis of proteins... [Crick, 1958, 138]
The Central Dogma... states that once ‘information’ has passed into
proteinit cannot get out again. In more detail, the transfer of informa-
tion from nucleic acid to nucleic acid, or from nucleic acid to protein
may be possible, but transfer from protein to protein, or from protein
to nucleic acid is impossible. Information means here theprecisede-
termination of sequence, either of bases in the nucleic acid or of amino
acid residues in protein. [Crick, 1958, 153]It is important to quote Crick’s full statement, not only because it had obtained
such a central role in molecular genetic thinking, but also because often it was
quoted in a distorted form. This was the case especially when reverse transcription
from DNA to RNA was discovered, when there were assertions such as “Central
dogma reversed”. Although Crick agreed that the term ‘dogma’ may have been
too strong, obviously “[t]he central dogma was put forward when much of what
we now know in molecular genetics was not established.... In such a situation
well constructed theories can play a really useful part in stating problems clearly
and thus guiding experiments” [Crick, 1970]. Notwithstanding, the notion that