THE BOOK OF POULTRY. 



Type. — This is not a unit quality, as it 

 depends upon {a) the shape of the body and (/>) 

 the nature and distribution of the feathers. 



Colour. — Very little is known ; dominance 

 depends upon the breed rather than upon the 

 colour ; the white of the Leghorn is dominant, 

 whilst that of the Silkie is recessive. Blue is 

 heterozygous in Andalusians and probably so in 

 the newer breeds. In certain blue varieties of 

 game it is said to be homozygous. 



Red ear-lobe. — Imperfect dominant. 



Eye colour. — Black is dominant. 



As the light thrown by Mendclism on the 

 problems of Heredity grows greater, fanciers will 

 be obliged to modify their views on certain 

 points (this we have already seen in the case 

 of purity and pedigree), and to express other 

 phenomena in Mendelian terms ; prepotency, 

 for e.xample, will have to be expressed in terms 

 of dominance. Mendclism does not so much 

 do away with the old ideas as give a working 

 hypothesis which explains them, and puts on 

 a scientific basis what before was more or less 

 " rule of thumb." 



Pi-epotcncy. — It was thought that a bird bred 

 for many generations for certain qualities would 

 be able to transmit them in a greater degree 

 than other birds bred for a shorter time ; but 

 now it is known that dominance of the charac- 

 teristic, and not a long pedigree, determines the 

 " prepotency." Thus pedigree will be valued 

 only by the nature of the gametes formed. 



Reversion. — It is a common occurrence for 

 breeders to find that one bird reproduces an 

 original ancestral form. This happens when, 

 through the addition or subtraction of a cer- 

 tain factor or factors, the elements are the same 

 as those in the constitution of the original bird. 

 This often happens when fresh blood is intro- 

 duced from a different strain by means of which 

 the complementary factors are brought together. 



A variety may be line-bred for twenty years 

 and in the twenty-first (certain new forms, not 

 reversions to any ancestral forms) 

 Sports make their appearance ; such new 



forms are termed " Sports." They 

 are probably due to the subtraction of a positive 

 factor or the omission of an inhibiting factor. In 

 the first case a certain characteristic is omitted ; 

 in the second a new one, hitherto prevented 

 from appearing, asserts itself 



Certain characteristics always seem to be 

 associated together in the same bird, the one 

 never being found without the other. 

 Correlation or \^ the relationship real or accidental .' 

 of factors'" Without strong evidence in support 

 of the first alternative, it is difficult 

 to believe that the independent submission to 



the laws of Heredity, which we found to be 

 characteristic of the different allelomorphic 

 pairs, does not hold good for all such pairs. 

 The eminent leader of the Mendelian School in 

 England is however of opinion that between 

 certain factors this relationship is real. 



Reciprocal crosses do not give identical 

 results. This is most clearly seen by crossing 

 light and heavy breeds both ways. 

 Sex-limited The offspring resembles the maternal 

 inheritance side in size, broodiness, and egg- 

 colour. Prof. Bateson and Mr. 

 Punnett found a case of sex-limited descent, 

 in the inheritance of pigment, in the reciprocal 

 crosses between brown Leghorns and Silkies. 

 This accounts for some of the anomalies met 

 with in the course of breeding, eg., the diffi- 

 culty of obtaining good legged females in 

 Wyandottes. No doubt certain sayings current 

 in the fancy have a scientific foundation. 



It looks as if certain characters are never 

 found in combination, e.g., prolificacy and ex- 

 cellence of table qualities ; yellow 

 bmty ^* ^' shanks and absolute soundness of 

 black plumage, etc. What the in- 

 compatibility is due to it is impossible at present 

 to state. 



There are very many interesting phenomena 

 which we should like to be able to explain, 

 such as Dimorphism, hen-feathered male birds, 

 etc. If the idea that our domestic fowls are 

 all descended from the Callus Bankiva (single 

 comb, white egg) is correct, it would be inter- 

 esting to know at what time and by what means 

 the factors for other combs were introduced ; 

 how and why tinted egg-shells appeared, etc. A 

 full solution of all these problems may be too 

 much to expect, but Mendclism supplies the 

 methods by which the problems of Heredity and 

 Variation can be solved. 



BIBLIOGRAPHY 



(i) " Mendel's Principles of Heredity." By 

 W. Bateson. Camb., 1909. Price 12,-. This is 

 the most complete and authoritative work in the 

 English language. 



(2) " Mendclism." By R. C. Punnett. Bowes 

 and Bowes, Camb. (2nd Edn.) 1909. 2/6. A 

 short and clearly written introduction to the 

 subject. 



(3) Reports to the Evolution Committee of 

 the Royal Society. Four numbers. 



(4) " Inheritance in Poultry." By C. B. Daven- 

 port Washington. 



(5) "The Laws of Heredity." By G. Arch- 

 dall Reid. Methuen, 1910. Useful survey of 

 theories up to date. 



