Biology Reference
In-Depth Information
in his
Essay on heredity and kindred biological problems
(1891)
Weismann dismantled the theory of gemmules and the inheritance
of acquired characteristics, then put forward his own theory. It pos-
tulates the complete separation of somatic cells (the body) and
germinal cells (reproductive gametes), the latter supposed to be the
only ones responsible for heredity.
“In these animals the power of reproduction is connected with
certain cells which, as germ cells, may be contrasted with those
which form the rest of the body; for the former have a totally dif-
ferent role to play; they are without significance for the life of the
individual, and yet they alone possess the power of preserving the
species. Each of them can, under certain conditions, develop into
a complete organism of the same species as the parent, with every
individual peculiarity of the latter reproduced more or less com-
pletely”
(EH p. 73).
More precisely, for Weismann, heredity is due to the transmis-
sion of a particular molecular structure contained in the germinal
cells, which he called the 'germ-plasm' and which prefigures our
DNA. “
I propose to call it the theory of 'The Continuity of the
Germ-plasm,
'
for it is founded upon the idea that heredity is brought
about by the transference from one generation to another, of a sub-
stance with a definite chemical and above all molecular constitution
”
(EH p. 170).
There are several important points in this founding hypothesis
which condition the entire coherence of genetics, including its cur-
rent developments. The first is the separation of the 'soma' and the
'germ-plasm' which prevents reproduction being influenced by the
organismic context or the environment. This separation has been
continued into modern genetic theory with the two concepts of the
phenotype and genotype: the phenotype is the actual organism,
corresponding to a set of characteristics controlled by the geno-
type, which corresponds to the set of genes. Reproduction of the
phenotype-body does not occur from the organs as in Hippocratic
theory, but through the intermediary of the genotype carried on the
