138 REPORT OF THE CONFERENCE ON GENETICS. 
DOMINANCE OF CHARACTERISTICS IN POULTRY. 
By Professor DAVENPoRT, Station for Experimental Evolution, 
Cold Spring Harbor, Long Island, U.S.A. 
Accorp1NnG to Mendel’s first principle, when two opposed characteristics 
(allelomorphs, Bateson) meet in hybridisation, one only appears in the 
offspring ; this character is called dominant, while the occluded charac- 
teristic is called recessive. The question is: What determines which 
of the two characteristics shall dominate? Is there any general law of 
dominance ? 
Three hypotheses have been formulated. First, it has been suggested 
by de Vries and others that the allelomorph belonging to the older species 
dominates. But this cannot be a general law, for it implies that all of 
the characteristics of the one species shall dominate over all those of 
the other species, and this is certainly not usually true. Second, Correns 
has concluded that, in general, the phylogenetically more advanced 
characteristic—the later originated, younger characteristic—dominates. 
Third, there is an hypothesis proposed by de Vries, and based upon his 
dictum that a variety differs from the parent species in that at least one 
characteristic of the species has become latent in the variety. Then, 
when an individual having a certain characteristic patent is crossed with 
one in which that characteristic is latent, the patent characteristic is 
dominant; the latent, recessive. 
The two latter hypotheses have been tested on poultry, a group that 
shows a great number of allelomorphs. ‘To test the Correns hypothesis 
the older and newer allelomorphs are placed opposite each other in 
parallel columns and the dominant characteristics are italicised. 
Old Characteristics New Characteristics 
1. Single comb. Pea comb. 
2. Single comb. Rose comb. 
8. Low nostril. High nostril. 
4, Plain skull. Cerebral hernia. 
5. Plain head. Crest. 
6. No muffling. Muffling. 
7. Plain feathers. Frizzled feathers. 
8. Non-silkiness. Silkiness. 
9. White skin. Black skin. 
10. Red iris. Black iris. 
11. Black plumage. White plumage. 
12. Red plumage. Black ; no red. 
13. Shafting No shafting. 
14. Pencilling. No pencilling. 
This table shows that, out of fourteen characteristics, five old ones 
are dominant and nine new ones. Clearly, dominance in poultry is not 
determined by the age of the characteristic. 
