CONCERNING PREPOTENCY 
The Idea Belongs to Practical Live-Stock Breeders, Not to Geneticists—How 
Prepotency May be Obtained by Breeders—How It 
May Be Explained By Geneticists. 
THE EpIToR 
The term “prepotency”’ is one which 
originated among practical breeders, not 
geneticists. It is a descriptive term 
which has been found useful for covering 
a number of different, but related, facts. 
It has the further merit, scientifically, 
that it describes these facts without 
implying adhesion to any hypothesis 
which, in its application to these facts, 
has not yet been proved. 
It is as a descriptive term that live- 
stock breeders habitually use the word, 
and it is in this sense that I used it in 
writing about Brigham Young; An Illus- 
tration of Prepotency, in the February 
issue of this journal. 
A member of this association, who 
prefers to remain anonymous, writes that 
he is ‘greatly moved”’ by the article, 
which ascribes the quality of prepotency 
to Brigham Young; first because he 
doubts whether my use of the term pre- 
potency is correct and second because 
he doubts whether on the evidence pre- 
sented Brigham Young had the superior 
influence as a parent which has been 
ascribed to him. As prepotency is a 
subject of general interest and of first 
importance to stock breeders as well as 
to students of genetics, it is worth while 
to give it further consideration. 
First let us decide what prepotency 
means. The Century Dictionary is in 
accord with the usage of the breeders 
when it defines the word as meaning 
“preeminent in power, influence, force 
or efficiency; prevailing; predominant.” 
As applied to heredity the dictionary 
says it would mean of superior power or 
influence in hereditary transmission, as a 
quotation cited from Darwin shows. If 
we turn to Darwin’s discussion of the 
subject in Animals and Plants, we find 
that he was unable to formulate any 
general rules concerning prepotency, 
superior influence seeming to inhere 
(1) in some cases in one character as 
330 
against a contrasted one (cases we should 
now describe as due to Mendelian domi- 
nance), while in other cases superior 
influence seemed to inhere (2) in one sex 
(cases which he described as sex-limited 
inheritance and which are now known 
to form a special category of Mendelian 
inheritance). In still other cases (3) 
Darwin believed one race or species to 
have superior influence in crosses with 
another race or species. 
DARWIN'S EXAMPLES 
As examples which we should place in 
category (1) Darwin mentions “purple- 
blossomed”’ peas as prepotent in crosses 
with ‘‘white-blossomed,” and fowls of 
normal plumage as prepotent in crosses 
with silkies. Fantail pigeons he regards 
as lacking prepotency in crosses with 
pouters and barbs, yet records the oc- 
currence of a silky sub-variety of fan- 
tails which invariably transmits its silky 
feathers in crosses. Hence lack of pre- 
potency does not inhere in fantails as 
regards all their characters but only as 
regards their fantail character. Other 
examples belonging in our category (1) 
noted by Darwin are dun color in horses, 
dark spotting in sheep, hornlessness in 
cattle, normal flowers of the snap- 
dragon and of Linaria in crosses with 
peloric flowers. 
As examples which we should place in 
category (2) Darwin mentions color- 
blindness in man, ‘‘the hemorrhagic 
diathesis’”’ (haemophilia?) and certain 
plumage characters of poultry and 
pigeons more often transmitted by 
males than by females. 
As examples of category (3) Darwin 
mentions the ass as prepotent in crosses 
with the horse, ‘‘the prepotency in this 
instance running more strongly through 
the male than through the female ass, 
so that the mule resembles the ass more 
strongly than does the hinny.” He 
