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Updated: May 19, 2025
And he concludes "that those who regard the thesis of the theory of order as necessary for everything that is or can be, must accept theism, and are not allowed to speak of 'dieu qui se fait." It is difficult to see how anyone who has studied the rigid order exhibited by experiments on Mendelian lines can resist the logic of this argument unless indeed he takes a place on Plate's platform, which admits that a law entails a lawgiver, but declares that of the Lawgiver of Natural Laws we can know nothing.
It is to be noted here, a fact emphasised by DeVries in his earliest publications on the subject, that in nearly all, if not all cases, a mutation does not consist in a peculiarity of a single organ, but in an alteration of the whole plant in every part. In this respect mutations as observed in Oenothera seem to be in striking contrast to the majority of Mendelian characters.
If the Mendelian law held good in this regard, from a union of a defective and a normal person, three out of four would be normal, but as a matter of fact, the percentage of normal is no doubt much greater. It is only when both father and mother are feeble-minded that feeble-mindedness is sure to show in the offspring.
Mutation in fact seems to be a case of what the earlier Darwinians called correlation, while Mendelian characters may apparently be separated and rejoined in any combination. For example, in breeds of fowls any colour or any type of plumage may be obtained with single comb or with rose comb.
There are facts, however, which prove that all species are not sterile inter se, and that their characters when they are hybridised do not always segregate in Mendelian fashion. Exper. In the former cross he states that except for one or two characters there seemed to be no more tendency to variation in the F2 generation than in the F1. The statement is, however, open to criticism.
But as regards the laws of heredity there is something else to be said; for here we really do know something, and that something we owe in large measure to the innumerable experiments which have been made on Mendelian lines since the re-discovery of the methods first adopted by the celebrated Abbot of Brünn.
The meaning of a recessive character in Mendelian terminology is one that is hidden by a dominant character, and both of them are due to factors in the gametes, particularly in the chromosomes of the gametes which come together in fertilisation. For example, in fowls rose comb is dominant over single.
Those sons inherit from their mothers as well as from their fathers, and the bad strain is often sufficient to obscure and nullify the good strain. Mediocrity, as every Mendelian knows, is a dominant character, and extraordinary ability is recessive character.
If they are of the same type, they may reinforce each other: if not, inhibitions and compensations will come into play. Mendelian laws may apply. The process of evolution, as the play of natural selection upon these variations, becomes comprehensible from a new standpoint.
Definite consequences follow in the constitution of the offspring; and such is the Mendelian contribution to heredity. But we must see that these inquiries cannot be far pursued without telling us vastly more than we ever knew before of not only the relation between individuals of successive generations, but the very structure of the individuals themselves.
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