576 GENETICS IN RELATION TO AGRICULTURE 
allelomorphic pair shall be dominant or recessive; and that this influence 
becomes stronger when large sets of factors determine a particular 
character. 
Greater Prepotency of the Male.—There has been a decided tendency 
to credit the male with greater prepotency than the female. Many 
investigators have pointed out that extra-biological influences such as 
the more rigid choice of males and the greater opportunity they have 
for impressing offspring may account for this belief among animal 
breeders. Some of the statistical evidence which Pearson has collected 
on this point seems to indicate no constant behavior in this respect. At 
the same time it should be noted that phenomena of sex-linkage and 
crossing-over may play an important réle here. The operation of the 
former we see in Pearl’s investigations of fecundity in fowls. Here the 
male is obviously the more prepotent with respect to the transmission 
of fecundity. The operation of the latter we see in Drosophila experi- 
ments Here there is no crossing-over in the male, as a consequence of 
which hybrid males more often transmit the particular set of factors 
which determine a phenotype like their own than do hybrid females. 
While the possibility of extending this phenomenon to mammals appears 
to have been destroyed by Castle’s work with rats, which demonstrated 
the occurrence of crossing-over in the male, nevertheless as a possible 
factor in relative prepotency of the sexes it should not be ignored. 
Conclusions with respect to prepotency. For the present then we 
must regard prepotency as an established fact, a phenomenon which has 
not yet been subjected to scientific analysis. From a biological stand- 
point, however, it is clear that even with our present restricted knowledge 
there is room for prepotency based upon the existence of different kinds 
of relations between factors. 
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