Full text: Problems in eugenics

40Section I.V. G. Ruggeri. 
heterozygote mice with each other there are four possibilities in the offspring : 
one of which is that of having the male and the female gamete with the 
same white determinant, therefore the zygote (i.e., the fecundated ovum) 
is homogeneous for such character, and the individual which results, from it 
is homozygote, as it is homozygote in the other possibility of the male and 
female gamete with the same grey determinant; one half of the offspring is 
in turn heterozygote, but nevertheless grey, this being the dominant 
character, while the character of whiteness is latent. 
The result is : if we cross grey homozygote mice with each other all the 
offspring are grey (and naturally homozygote as the progenitors); if instead 
we cross grey heterozygote mice there will be 25 per cent, of white mice 
amongst the offspring. 
If one of the heterozygote grey mice is crossed with a white mouse, 
inasmuch as this last has only gametes with a white determinant and the 
former has instead two opposed determinants (grey and white), there are two 
possibilities—either the grey meets the white or the white meets the white, 
in the former case we get a grey mouse (heterozygote), in the second case a 
white mouse. That is to say, half of the offspring are white. 
The successive generations behave in the same manner, so, to sum up, 
white, as the dominant character, is always homozygote from the moment 
which cannot be evident except when its opposed dominant—i.e., grey—is 
completely wanting both in the somatic cells and in the germ cells. 
In many other albino animals the same rules have been found which will 
find their verification also in human albinos, since the Davenports have 
succeeded in proving that two albino parents have only albino children(i). 
Still more important is the fact proved by the same Gertrude and Carlo 
Davenport, that if one only of the parents is albino 50 per cent, of the 
children are albino. That implies that the other parent, although normally 
pigmented, behaves like the heterozygote grey mouse, i.e., with the albino 
character remaining latent. And this is precisely the explanation given by 
the Davenports. This explanation is also implicitly valid for albinos born 
of parents both of whom are pigmented, i.e., that both these parents must 
possess the character of albinism a9 a recessive: in such a case it could only 
appear once in four children, according to that rule of 25 per cent, which 
we have seen for the offspring of two heterozygote grey mice. 
The Davenports in their very extensive researches have had instead an 
average of 34 per cent., but that is explained by them by the fact that the 
reporters easily omit a normal child, rather than an abnormal one, as the 
abnormal one is just the special object of the inquiry. It can also be 
asserted that 33 per cent, of these same families showed consanguinity of 
parentage, whence it is evident that the latent character, i.e., albinism, came 
to them from a common ancestor, and that is probable in many other cases 
(1) G. C. and C. B. Davenport, Heredity of Skin Pigment in Man. American Naturalist 
XLIV. (1910), Nov.-Dee., p. 727-

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