have generated by highlighting the obser-
vation common to the vast majority of
hybridizing plant and animal taxa (as
well as for those organisms exchanging
genes via viral recombination and lateral
exchange), that hybrid genotypes
demonstrate a range of fitness estimates
that are often affected by the environ-
ment. This key observation leads to an
array of expectations concerning the
challenges faced in forming hybrid
lineages—both under [i.e., under both]
natural and experimental conditions.
Furthermore, the observation of a wide
range of hybrid fitness should also
lead to caution during the generation of
predictions concerning the effects on
natural ecosystems from the introduction
of bio-engineered plant lineages.To Where Are We Going?I am reminded of the Old Testament
mandate that states that prophets, once
proven inaccurate, were to be stoned.
In that context, I offer the following sug-
gestion concerning one direction I
believe studies of genetic exchange (of
which I do consider myself a student)
and plant biotechnology (of which I do
not) should be progressing. The analyses
of genetic exchange, across all taxo-
nomic categories, are entering anexciting phase. The definition of the
genomic architecture of related organ-
isms allows the dissection of the causal
factors that affect the transfer of
specific loci. Given such information, it
is possible to state with some certainty,
which loci are prevented and which
loci are facilitated in their transfer
between organisms belonging to diver-
gent evolutionary lineages. However, a
more difficult, and much more signifi-
cant, inference is needed. Specifically,
it is necessary to define the “why”
behind a transfer (or lack of transfer).
In other words, what is the specific
effect on the organism that causes
either an increase in the fitness of
hybrid genotypes (leading to genetic
transfer) or a decrease in the fitness of
hybrid genotypes (resulting in no trans-
fer) when certain combinations of loci
are present? The degree to which we
are able to address and answer this ques-
tion, will be the degree to which we are
able to test hypotheses concerning such
fundamentally important processes
as (i) the effect of genetic exchange
on hybrid lineage formation and the
transfer of adaptations and (ii) the
impact of genetic exchange between
bio-engineered plants and wild relatives
on both crop production and natural
ecosystems.References
Anderson E (1953): Introgressive hybridization.Biological Reviews 28 :280–307.
Bateson W (1909):Mendel’s Principles of Heredity. Cambridge Univ. Press, Cambridge, UK.
Bridges CB (1916): Nondisjunction as a proof of the chromosome theory of heredity.Genetics 1 :
1–52, 107–163.
Bridges CB (1925): Sex in relation to chromosomes and genes.Am Nat 59 :127–137.
Briggs D, Walters SM (1997):Plant Variation and Evolution, 3rd ed. Cambridge Univ. Press,
Cambridge, UK.
Camerarius RJ (1694): Epistola ad M.B. Valentini de sexu plantarum. In Ostwald’s Klassiker der
exakten Naturwissenschaften, No. 105, 1899. Verlag von Wilhelm Engelmann, Leipzig.
Darwin CR (1876):The Effects of Cross and Self Fertilisation in the Vegetable Kingdom. John
Murray, London.
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