Biology Reference
In-Depth Information
The contradiction in genetic determinism was, in fact, evident
in the earliest work by classical geneticists.
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The evolution which
Morgan's work underwent illustrates this in a remarkable way: he
was obliged to considerably modify his initial theory because of
the results of his own research. First of all, he had reaffirmed a
form of genetic determinism identical to Weismann's. His position
was very radical. His belief in the causal ability of genes led him
to put the importance of embryonic development into perspec-
tive. He thought that the relationship between the genes and phe-
notypic characteristics was completely determined; knowledge of
this relationship was enough in itself to manipulate phenotypic
characteristics, without knowing the mechanisms of embryonic
development. In his topic
The Theory of the Gene
(1926), he
asserted:
“The theory states that the characters of the individual are refer-
able to paired elements (genes) in the germinal material that are
held together in a definite number of linkage groups… (…) The
theory of the gene, as here formulated, states nothing with respect
to the way in which the genes are connected with the end-product
or character. The absence of information relating to this interval
does not mean that the process of embryonic development is not of
interest for genetics. A knowledge of the way the genes produce
their effects on the developing individual would, no doubt, greatly
broaden our ideas relating to heredity, and probably make clearer
many phenomena that are obscure at present… (…) There is, nev-
ertheless a fundamental assumption implied in the statement just
made, viz., that the development follows strictly causal laws. A
change in a gene produces definite effects on the developmental
process. It affects one or more of the characters that appear at
some later stage in the individual.
In this sense, the theory of
the gene is justified without attempting to explain the
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Before molecular biology, classical geneticists studied the transmission of
characteristics independent of the underlying mechanisms.
