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
These circumstances do not appear to have been known to Mr Knight, as
he seems to have carried on his experiments by continuing to cross
his seedlings in the year succeeding their production from a cross
and treating the results as reliable; whereas it is probable that the
results might have been materially affected by the disturbing causes
then in existence arising from the previous cross fertilisation, and
which, I consider, would, in all cases where either parent has not
become fixed or permanent, lead to results positively perplexing
and uncertain, and to variations almost innumerable. I have again
selected, and intend to sow, watch, and report; but as the usual
climax of variation is nearly reached in the recorded experiment, I
do not anticipate much further deviation, except in height and period
of ripening--characters which are always very unstable in the pea.
There are also important botanical and other variations and changes
occurring in cross-fertilised peas to which it is not my province
here to allude; but in conclusion I may, perhaps, in furtherance of
the objects of this paper, be permitted to inquire whether any light
can, from these observations or other means, be thrown upon the origin
of the cultivated kinds of peas, especially the “maple” variety, and
also as to the source whence the violet and other colours which appear
at intervals on the seeds and in the offspring of cross-fertilised
purple-flowered peas are derived.”
The reader who has closely followed the preceding passage will begin
to appreciate the way in which the new principles help us to interpret
these hitherto paradoxical phenomena. Even in this case, imperfectly
recorded as it is, we can form a fairly clear idea of what was taking
place. If the “round” seeds really occurred as a distinct class, on
the heterozygotes as described, it is just possible that the fact may
be of great use hereafter.
We are still far from understanding maternal seed-form--and perhaps
size--as a dominant character. So far, as Miss Saunders has pointed out
to me, it appears to be correlated with a thick and coloured seed-coat.
* * * * *
We have now seen the nature of Professor Weldon’s collection of
contradictory evidence concerning dominance in peas. He tells us:
“Enough has been said to show the grave discrepancy between the
evidence afforded by Mendel’s experiments and that obtained by
observers equally trustworthy.”
Public-domain text, read in full here on John Shaqi.
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