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
In 1868 I sowed the peas of the preceding year’s growth, and selected
various plants for earliness, productiveness, &c. Some of the plants
had light-coloured stems and leaves; these all showed white flowers,
and produced round white seeds[110]. Others had purple flowers, showed
the purple on the stems and at the axils of the stipules, and produced
seeds with maple, grey, purple-streaked, or mottled, and a few only,
again, with violet-coloured envelopes. Some of the seeds were round,
some partially indented[111]. The pods on each plant, in the majority
of instances, contained peas of like characters; but in a few cases
the peas in the same pod varied slightly, and in some instances a
pod or two on the same plant contained seeds all distinct from the
remainder[112]. The white-flowered plants were generally dwarfish,
of about the height of “Ringleader”; but the coloured-flowered sorts
varied altogether as to height, period of ripening, and colour and
shape of seed[113]. Those seeds with violet-coloured envelopes produced
nearly all maple- or parti-coloured seeds, and only here and there one
with a violet-coloured envelope; that colour, again, appeared only
incidentally, and in a like degree in the produce of the maple-coloured
seeds[114].
[110] Recessive in flower-colour, seed-coat colour, and in seed-shape
as a maternal character: pure recessives as the sequel proved.
[111] These are then a mixture of pure dominants and cross-bred
dominants, and are now inextricably confused. This time the round
seeds may have been all on particular plants--showing recessive
seed-shape as a maternal character. It seems just possible that
this fact suggested the idea of “round” seeds on the _coloured_
plants in the last generation. Till that result is confirmed it
should be regarded as very doubtful on the evidence. But we cannot
at the present time be sure how much difference there was between
these round seeds and the _normal_ maples in point of shape; and
on the whole it seems most probable that the roundness was a mere
fluctuation, such as commonly occurs among the peas with large
indented seeds.
[112] Is this really evidence of segregation of characters, the
flower being the unit? In any case the possibility makes the
experiment well worth repeating, especially as Correns has seen a
phenomenon conceivably similar.
[113] Being a mixture of heterozygotes (probably involving several
pairs of allelomorphs) and homozygotes.
[114] This looks as if the violet colour was merely due to
irregularity of xenia.
Public-domain text, read in full here on John Shaqi.
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