Slocum: Poultry Breedinsf 



485 



haps the best known example of sex 

 limited inheritance is the barred color 

 pattern of the Barred Plymouth Rock, 

 which seems to occur in accordance with 

 a mendelian hypothesis developed along 

 lines first suggested by Spillman. 



The female, by this hypothesis, is 

 considered to be heterozygous both for 

 sex and for barring while a repulsion is 

 assumed between the determiners for 

 these two characters which prohibits 

 their occurrence in the same gamete. 

 The male is considered to be homozygous 

 in respect to sex and either homozygous 

 or heterozygous in respect to barring. 

 The females, therefore, inherit barring 

 from their sire alone. A number of 

 different crosses have been made and 

 reported which support this hypothesis, 

 e.g., Black Langshan and Barred 

 Plymouth Rocks, Cornish Indian Game 

 and Barred Rock, White Cochin and 

 Tosa, and Barred Plymouth Rocks 

 with Campines, with Golden Pencilled 

 Wyandottes, with Black Hamburg, with 

 White Wyandottes and with White 

 Plymouth Rocks. 



Sex-linkage has been reported in a 

 mmiber of other instances, such as an 

 inhibiting factor influencing the meso- 

 dermal pigmentation of the Silky, 

 Brown Leghorn color pattern, an inhibi- 

 tion for red in the plumage carried by the 

 Columbian Wyandotte, the gray of the 

 White Wyandotte and the factor on 

 which high fecundity depends. 



INHERITANCE OF EGG PRODUCTION 



For about nine years, from 1898 to 

 1907, at the Maine Agricultural Experi- 

 ment Station, a systematic breeding 

 experiment was carried on in an effort to 

 increase the average egg production of 

 the Station's poultry stock. The plan 

 of the experiment was to select breeders 

 upon the basis of their performance 

 alone as shown by the trap nest. It was 

 expected that the high production would 

 be handed down from mother to 

 daughter and that the selection prac- 



- The conclusions of the Maine station are based on the belief that high egg production is a unit 

 character. But the results of eight years work at the Utah station, presented by E. D. Ball and 

 Byron Alder at the last meeting of the American Genetic Association, but not yet published, fail 

 to confirm this conclusion. The twenty-seventh annual report of the Massachusetts Agricultural 

 Station, summing up the studies on egg-production there, also indicates a belief that high egg pro- 

 duction is a compound, not a simple, trait. The question probably must be considered an open 

 one for the present. 



ticed would be cumulative in its effect. 

 Indeed it was generally supposed that a 

 substantial increase in the average egg 

 yield had been obtained -but a complete 

 and searching analysis not only failed 

 to reveal such an increase but actually 

 showed a slight decrease since the 

 beginning of the experiment. 



In 1907 the plan of procedure was 

 changed and one of the steps taken was 

 to cross the original stock of the station, 

 the Barred Plymouth Rock, a breed of 

 relatively good laying ability, with the 

 Cornish Fowl, a breed of relatively 

 poor laying ability. A study of the 

 inheritance of fecundity in these cross- 

 bred individuals and in other matings 

 resulted in the hypothesis advanced by 

 Dr. Raymond Pearl, that the factor 

 responsible for high egg production 

 behaved as a sex-limited character. 

 According to this hypothesis, the female 

 is heterozygous for sex and also for the 

 factor for high fecundity and these two 

 factors cannot be present in the same 

 gamete. It follows therefore that a 

 daughter cannot inherit high fecundity 

 directly from her dam but must always 

 inherit it, if present, from her sire. 

 She may, however, inherit low fecundity 

 from either dam or sire or from both.^ 



PRACTICAL RESULTS 



The application of Mendelism to 

 poultry breeding holds out not the 

 slightest hope of creating new characters. 

 It does, however, point out the way to 

 secure new combinations of desired 

 characters by crossing varieties or 

 breeds possessing them and by careful 

 breeding to fix this combination in one 

 breed or variety. In so far as a pair of 

 characters behave as a strictly repre- 

 sentative Mendelian pair, one of which 

 shows complete dominance over the 

 other, the application of Mendelism to 

 poultry breeding \vill prove an advantage 

 in poultry work as it will often provide a 

 short cut to the desired end by providing 

 a quicker means of testing out the purity 



