MENDELISM AND ITS APPLICATION TO POULTRY BREEDING 



13 



written four times horizontally, and the four 

 combinations of the second pair are written four 

 times vertically. 



An examination of the above diagram shows 

 that in nine cases (Fig. a) the dominants rose 

 and feathers appear together ; in three cases 

 {Fig. c) rose and silk are found together, in 

 another three cases (Fig. d) feathers and single 

 are found, while one bird in 16 (Fig. b') has 

 single comb and silk. This last forms a new 

 variety, the gametes formed being pure for 

 single comb and for silk. Out of these 16 

 combinations there are 4 visible types arranged 

 in the following arithmetical proportions : — 



9:3:3:1 



A consideration of the above will show what 

 has already been emphasised, that outward ap- 

 pearances are no real criterion of the breeding 

 value of any bird. Only the first RR FF and 

 the last ss yy are zygotes pure in both pairs 

 of characters. 



When three allelomorphic pairs are observed 

 together, a similar reasoning, or a mathematical 

 formula, will show that there are sixty-four 

 possible combinations, though in outward ap- 

 pearances there would be only eight types. 



To return to the well-known mating of rose 

 and single comb, in F, there were only two t}'pes 

 rose and single, but four combinations (one pure 

 rose, two impure rose, and one single). When 

 two allelomorphic pairs are considered, the num- 

 ber of types, as we have seen, is 2^ and the 

 number of possible combinations is 42. When 

 three pairs are taken together, the number of t)pes 



is 2'' and of combinations is 4''. With "n" 

 allelomorphic pairs the number of types visible 

 is 2" and of possible combinations 4". Complete 

 dominance is assumed here. 



According to Prof. Bateson, a fowl may be 

 regarded as a " basal organisation " upon which, 

 through the agency of certain 

 Characteris- (actors, a number of characteristics 

 a fowl have been built up or superimposed. 



What essentially is the " basal 

 organisation " we cannot tell. At present we 

 know very little of the action, or nature, of 

 the factors which induce the changes which 

 produce varieties. When we do, we shall 

 have a clearer knowledge of the origin of 

 species than we now possess. In the variations 

 observed among birds we can distinguish two 

 kinds : — (a) Fluctuations, or non-transmissible 

 varieties ; appearances which seem to be the 

 peculiar property of one individual. Probably 

 most of the scoring points of a show bird come 

 under this head, (b) Mutations or transmissible 

 variations ; changes which appear in response 

 to certain factors which form part of the in- 

 dividual and aie handed on to its progeny. 



Comb. — We have seen that rose is dominant 

 over single, i.e., that it is a single -j- some factor 

 which causes it to appear as rose. Most forms 

 of comb are dominant to single. Many ex- 

 periments have been and are being made, but 

 as long as we cannot satisfactorily explain 

 the appearances of side sprigs, etc., Genetics 

 has not completely read the riddle of the 

 comb. 



Size. — It is still a matter of doubt whether 

 size is an allelomorphic character. 



Fiftli toe. — This appears to be dominant ; 

 dominance is somewhat irregular, as it may 

 appear on one foot only, and there are cases 

 known of four-toed recessives transmitting it 

 to their progeny. 



Feathers on legs.- — This is dominant but its 

 transmission may be governed by two factors, 

 which would explain its appearance in the 

 progeny of two-cleaned birds of different strains 

 mated together. 



Crest and Muff. — Incomplete dominants, the 

 characters always appear but vary in size. 



Broodiness. — Dominant, the progeny always 

 show a tendency to sit, but are somewhat un- 

 certain and erratic and leave the chicks earlier. 



Colour of egg. — Brown is an incomplete dom- 

 inant, shade varying. 



Size 0/ egg.— An incomplete dominant. 



Prolificaey.—\t is doubtful whether it is a 

 dominant in any proper sense, but cross-bred 

 birds between light and heavy breeds are always 

 better layers than the heavy breeds. 



