MENDELISM AND ITS APPLICATION TO POULTRY BREEDING 



(D + R)(D + R) = DD + 2DR+RR. A consi- 

 deration of this will lead to the same conclu- 

 sion that has already been arrived at practically, 

 viz., that the result would give 25^0 pure domi- 

 nants, 50% impure dominants, and 25% pure 

 recessives. These results are usually represented 

 diagrammatically thus — D standing for the 

 dominant and R for the recessive char- 

 acter : — 



If the impure dominants are bred with a 

 dominant, they give 50^0 pure dominants and 

 50% impure dominants (D -|- D){D -f R) = 

 2DD-I-2DR; bred with a recessive, they give 

 50°o pure recessives and 50°^ impure dominants 

 (R-|-R){D-|-R)=2RR-h2DR. 



When the zygote formed by the union of 

 the male and female gametes has received the 

 same elements from each gamete, e.g. either 

 the dominant or the recessive character from 

 both, it is said to be homozj'gous, or a zygote 

 pure for that character ; when, on the other 

 hand, it receives one character from one gamete 

 and the other character from the other gamete, 

 it is termed heterozygous, or a zygote impure 

 for that character. 



In Mendel's experiment given above, each 

 parent is pure, F, is heterozygous. In F^,, 50% 

 are homozygous (i.e., 25°o homozygous for tall- 

 ness and 2590 homozygous for dwarfness) and 

 50% are heterozygous, impure zygotes contain- 

 ing both characters. 



This experiment of Mendel's which we have 

 just considered, illustrates clearly his method, 

 which is essentially simple. It is applicable to 

 all allelomorphic characters in every species of 

 animals and plants. Mendel himself investigated, 

 in peas alone, seven distinct allelomorphs (pairs 

 of characters^. 



The pioneers in the re-establishment of the 

 methods of Mendel are De Vries, Corrcns, 

 Tschermak, and in England, Bate- 

 Mendelism son. The work has been carried 

 and Poultry on with plants and animals. As 

 breeders of poultry, we are here 

 only concerned with the work that has been 

 accomplished in our own domain. Results will 



be given briefly, as a full discussion of each 

 case would carry us beyond the limits of this 

 chapter. What is given will be found suffi- 

 ciently suggestive for those who may v/ish to 

 repeat the experiments, or to devise others of 

 their own, in which they can follow the course 

 of heredity in one or more selected characters. 

 Fanciers are as a rule very keen on experi- 

 mental matings ; a great deal of work of this 

 kind has been done, and undoubtedly much 

 useful knowledge has been lost because the 

 results of these matings have not been put on 

 record. The field of investigation is a vast 

 one ; the scheme of coloration alone covers a 

 wide area, and it will probably be some time 

 before it is fully explored. Little has been 

 achieved as )-ct, but sufficient has been done 

 to show that Mendclism offers a method by 

 which the problems can be solved. Every 

 result established assists the breeder in his 

 labours, and he can proceed with certain know- 

 ledge as far as an investigated character is con- 

 cerned. 



The simplest illustration of the application 

 of the principles of Mendclism to the breeding 

 of poultry is seen by crossing a rose-comb with 

 a single-comb bird. It is a matter of common 

 knowledge that the result of such a mating is 

 rose-comb progeny, and Mendclism enables us to 

 explain these facts. Rose is evidently dominant 

 over single, just as tallness was dominant over 

 dwarfness. If the experiment is continued 

 and the rose-comb F, generation is bred inter se, 

 we get 75% rose to 25% single, and of these 

 75''r. rose one-third or 25% of the whole are pure 

 rose. In fact we get exactly the same behaviour 

 as in the case of tall and dwarf peas, only rosc- 

 ness takes the place of tallness, and single the 

 place of dwarfness. The result can be expressed 

 diagrammaticall)', R = rose and S ^=- single. 



Bred inter se 

 v/ith a pure r 



future generalii 



The type of rose-comb in Fj varies consider- 

 ably, some being almost as perfect as the 

 parental type, whilst others fall away consider- 

 ably from this standard of perfection. It is not 

 possible to distinguish the pure rose from the 

 impure by observation, the only real test is 

 breeding, and it does not follow that purity coin- 

 cides with perfection of comb. To test which 



