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 what has been said it will now be clear that the applicability of
the Mendelian hypothesis has, intrinsically, nothing whatever to do
with the question of the inheritance being _blended_ or _alternative_.
In fact, as soon as the relation of zygote characters to gamete
characters is appreciated, it is difficult to see any reason for
supposing that the manifestation of characters seen in the zygotes
should give any indication as to their mode of allotment among the
gametes.
On a previous occasion I pointed out that the terms “Heredity” and
“Inheritance” are founded on a misapplication of metaphor, and in the
light of our present knowledge it is becoming clearer that the ideas of
“transmission” of a character by parent to offspring, or of there being
any “contribution” made by an ancestor to its posterity, must only be
admitted under the strictest reserve, and merely as descriptive terms.
* * * * *
We are now presented with some entirely new conceptions:--
(1) The purity of the gametes in regard to certain characters.
(2) The distinction of all zygotes according as they are or are not
formed by the union of like or unlike gametes. In the former case,
apart from Variation, they breed true when mated with their like; in
the latter case their offspring, collectively, will be heterogeneous.
(3) If the zygote be formed by the union of dissimilar gametes, we
may meet the phenomenon of (_a_) dominant and recessive characters;
(_b_) a blend form; (_c_) a form distinct from either parent, often
reversionary[20].
[20] This fact sufficiently indicates the difficulties involved in a
superficial treatment of the phenomenon of reversion. To call such
reversions as those named above “returns to ancestral type” would be,
if more than a descriptive phrase were intended, quite misleading. It
is not the ancestral _type_ that has come back, but something else
has come in its guise, as the offspring presently prove. For the
first time we thus begin to get a rationale of “reversion.”
But there are additional and even more significant deductions from the
facts. We have seen that the gametes are differentiated in respect
of pure characters. Of these pure characters there may _conceivably_
be any number associated together in one organism. In the pea Mendel
detected at least seven--not all seen by him combined in the same
plant, but there is every likelihood that they are all capable of being
thus combined.
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