Full text: Problems in eugenics

D. F. Weeks. Biology and Eugenics.63 
With epilepsy thus defined, we have endeavoured to learn what laws, if 
any, are followed in its return to successive generations; how often it 
arises de-nova in strains which show elsewhere no mental weakness; what 
relation it bears to alcoholism, migraine, paralysis, and other symptoms of 
lack of neural strength. 
Until recently it has been considered sufficient to determine the known 
number of epileptic ancestors or other relatives of a case of epilepsy, and 
then take this proportion as the index of heredity, with the natural result 
that the index increased as the study of the family was extended, resulting 
in a difference of from 20 to 75 per cent., as determined by different workers. 
In our study of the inheritance of epilepsy, we have endeavoured to 
analyze our data by the Mendelian method, which assumes that the in­ 
heritance of any character is not from the parents, grandparents, etc., but 
from the germ plasm out of which every fraternity and its parents and other 
relatives have arisen. 
The relation of soma and germ plasm is as follows :— 
1. If the soma possesses a trait of the recessive to normality sort, it lacks 
the unit character upon which normal development depends, and it is prima 
facie evidence that the representative of that character is absent from its 
germ plasm; consequently such a person cannot transmit the character in 
question. The condition in the case when the determiner is absent may be 
called nulliplex. 
2. If the soma possesses a trait of the dominant to normality sort, it is 
evidence that the germ plasm has the corresponding determiner. But either 
one of two conditions is possible: (a) The determiner was derived from 
both parents, so that it is double in the germ plasm, or duplex, and all the 
germ cells have the determiner; or else (b) it came from one parent only, 
in which case it is single in the germ plasm, or simplex, and half of the 
germ cells have and half lack the determiner. 
A moment’s consideration will show that six kinds of gametic matings, 
disregarding sex, are possible. These matings, together with the sort 
of conceptions they may be expected to yield, are as follows :— 
I. Nulliplex x Nulliplex = 
II. Nulliplex x Simplex 
III. IV.Nulliplex SimplexNormal Simplex 
V. Simplex x Normal = 
VI. Normal x Normal100% Nulliplex — without the 
character for full mental de­ 
50% with character Nulliplex; 
50% with it Simplex. 
100% with character Simplex. 
25% with character Nulliplex, 
50% with it Simplex; 25% 
with it Normal. 
50% with character Simplex; 
50% with it Normal. 
100% Normal—mentally strong.

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