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 sports appear to become fixed and permanent in the next
and succeeding generations; and the tendency to revert and sport
thenceforth seems to become checked if not absolutely stopped[141].”
[141] The combinations being exhausted. Perhaps Professor Weldon
thought his authority was here lapsing into palpable nonsense!
Now if Professor Weldon instead of leaving off on the word “ancestry”
had noticed this passage, I think his article would never have been
written.
Laxton proceeds:--
“The experiments also tend to show that the height of the plant
is singularly influenced by crossing; a cross between two dwarf
peas, commonly producing some dwarf and some tall [? in the second
generation]; but on the other hand, a cross between two tall peas
does not exhibit a tendency to diminution in height.
“No perceptible difference appears to result from reversing the
parents; the influence of the pollen of each parent at the climax or
fourth generation producing similar results[142].”
[142] Laxton constantly refers to this conception of the “climax”
of--as we now perceive--analytical variation and recombination. Many
citations could be given respecting his views on this “climax” (cp.
p. 167).
The significance of this latter testimony I will presently discuss.
Professor Weldon next appeals to a later paper of Laxton’s published in
1890. From it he quotes this passage:
“By means, however, of cross-fertilisation alone, and unless it be
followed by careful and continuous selection, the labours of the
cross-breeder, instead of benefiting the gardener, may lead to utter
confusion,”
Here again the reader would have gained had Professor Weldon, instead
of leaving off at the comma, gone on to the end of the paragraph, which
proceeds thus:--
“because, as I have previously stated, the Pea under ordinary
conditions is much given to sporting and reversion, for when two
dissimilar old or fixed varieties have been cross-fertilised,
three or four generations at least must, under the most favourable
circumstances, elapse before the progeny will become fixed or
settled; and from one such cross I have no doubt that, by sowing
every individual Pea produced during the three or four generations,
hundreds of different varieties may be obtained; but as might be
expected, I have found that where the two varieties desired to be
intercrossed are unfixed, confusion will become confounded[143],
and the variations continue through many generations, the number at
length being utterly incalculable.”
[143] Further subdivision and recombination of hypallelomorphs.
Public-domain text, read in full here on John Shaqi.
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