Mendel's principles of heredity: A defenceMendel, Gregor
Science
Mendel's principles of heredity: A defence
Mendel, Gregor
Heredity; Hybridization; Mendel's law; Weldon, Walter Frank Raphael. Mendel's laws of alternative inheritance in peas
From Mendel’s style it may be inferred that if he had meant to state
universal dominance in peas he would have done so in unequivocal
language. Let me point out further that of the 34 varieties he
collected for study, he discarded 12 as not amenable to his
purposes[81]. He tells us he would have nothing to do with characters
which were not sharp, but of a “more or less” description. As the
34 varieties are said to have all come true from seed, we may
fairly suppose that the reason he discarded twelve was that they
were unsuitable for his calculations, having either ill-defined and
intermediate characters, or possibly defective and irregular dominance.
[81] See p. 43.
IV. PROFESSOR WELDON’S COLLECTION OF “OTHER EVIDENCE CONCERNING
DOMINANCE IN PEAS.”
_A. In regard to cotyledon colour: Preliminary._
I have been at some pains to show how the contradictory results, no
doubt sometimes occurring, on which Professor Weldon lays such stress,
may be comprehended without any injury to Mendel’s main conclusions.
This excursion was made to save trouble with future discoverers of
exceptions, though the existence of such facts need scarcely disturb
many minds. As regards the dominance of yellow cotyledon-colour over
green the whole number of genuine unconformable cases is likely to
prove very small indeed, though in regard to the dominance of round
shape over wrinkled we may be prepared for more discrepancies. Indeed
my own crosses alone are sufficient to show that in using some
varieties irregularities are to be expected. Considering also that
the shapes of peas depend unquestionably on more than one pair of
allelomorphs I fully expect regular blending in some cases.
As however it may be more satisfactory to the reader and to Professor
Weldon if I follow him through his “contradictory” evidence I will
endeavour to do so. Those who have even a slight practical acquaintance
with the phenomena of heredity will sympathize with me in the
difficulty I feel in treating this section of his arguments with that
gravity he conceives the occasion to demand.
In following the path of the critic it will be necessary for me to
trouble the reader with a number of details of a humble order, but the
journey will not prove devoid of entertainment.
Now exceptions are always interesting and suggestive things, and
sometimes hold a key to great mysteries. Still when a few exceptions
are found disobeying rules elsewhere conformed to by large classes of
phenomena it is not an unsafe course to consider, with such care as
the case permits, whether the exceptions may not be due to exceptional
causes, or failing such causes whether there may be any possibility of
error. But to Professor Weldon, an exception is an exception--and as
such may prove a very serviceable missile; so he gathers them as they
were “smooth stones from the brook.”
Public-domain text, read in full here on John Shaqi.
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