MENDELISM AND ITS APPLICATION TO POULTRY BREEDING 



is a matter for investigation witli a tolerable 

 certainty that the secret, so far well guarded, 

 may be learnt and the Gordian knot of heredity 

 may be unravelled. The first step to this solu- 

 tion is the fact that parental characters are 

 transmitted to the offspring as units, and this 

 transference by " units " gives an intelligent 

 explanation of the regularity that has been 

 observed in cases that have been studied. The 

 unit character may be for some reason latent 

 in one generation, but may be transferred to 

 the next without the influence which inhibited 

 its appearance in the parents ; then it will re- 

 appear. Thus the grandchild may show some 

 character of a paternal or a maternal grand- 

 parent which was not apparent in the inter- 

 mediate generation. Other characters require 

 to be received from both parents before the\- 

 appear and so are latent until this condition 

 is fulfilled. The students of Genetics must 

 grasp the fact that the separate characters are 

 transmitted (or not transmitted) as unit charac- 

 ters. If the characters were not transmitted 

 as units but as indefinite '"ractions, then it would 

 be impossible to predict any result, as the 

 character would var}' in intcnsit}- according to 

 the value of the fractional part transmitted. 



.An individual bird should thus be regarded 

 as an aggregation of characters. These charac- 

 ters have been derived from two parents : the 

 dual nature of every individual must be com- 

 prehended before the principles of Mendelism 

 can be understood and applied in the process 

 of practical breeding. When the individual has 

 received a similar set of characters from each 

 parent, it is said to be pure bred ; when it has 

 received a set of characters from one parent 

 differing from the set derived from the other 

 parent, it is said to be impure or cross bred, 

 even though the differing characters may not 

 be apparent in the first generation, but remain 

 latent. For instance, cross a pure rose-comb with 

 a single-comb bird : all the offspring are rose-comb 

 but the rose is an impure rose and the bird 

 is a cross-bred in respect to comb. It is only 

 pure when it receives the elements of roseness 

 from each parent. The impurity will show 

 itself when these birds are inbred. We thus 

 get a definite meaning attached to pure bred 

 and cross-bred, a meaning which will bear the 

 test of breeding. 



Fanciers have in reality always regarded a 

 bird as an aggregation of characters. In breed- 

 ing a winner, the fancier has kept his eye on the 

 bird from beak to tail and from comb to toes, 

 and in judging it the bird has been examined 

 and weighed according to its excellence in all 

 the characters visible to the eye. The standards 



of excellence for the various breeds award 

 points for these outward characters. Mendelism 

 introduces the breeder to methods with which he 

 is familiar and which he has pursued in the 

 course of his labours. The principles of Men- 

 delism justify the methods he has employed, 

 and will enable him in future to place them on 

 a sound scientific basis. 



It is clear, then, that the individual is what 

 he is from the contributions he has received 

 from both parents, and thus it is true that 

 all individuals (not poets alone) are " born, not 

 made." These contributions have been made 

 through each gamete or germ cell, the one sup- 

 plied by the male, the other by the female. The 

 question can be legitimately asked, how much of 

 this machinery of the gamete is understood, and 

 how far can it be explained 1 In the present 

 state of Genetics the answer is that very little is 

 known of the actual machinery for the transfer- 

 ence of characters, i.e., of the internal arrange- 

 ment of the gamete. Prof Bateson has stated, 

 in reference to the probable constitution of the 

 factors which make up the gamete, that " several 

 of them behave much as if they were ferments, 

 and others as if they constructed the substances 

 on which ferments act." 



To understand the way in which the methods 

 of transference take place, it is necessary to 

 follow what happens in regard to 

 Segregation those characters which compose the 

 individual when it comes to repro- 

 duce its own species. The dual nature of the 

 individual must be borne in mind, viz., that its 

 characters have been derived from two sources. 

 It has been discovered that, in the formation of 

 the germ cells, the characters from each parent 

 are re-sorted and this re-sortment of the parental 

 characters, during the lormation of the gametes 

 in the individual, is the central fact in Mendelism 

 and it is termed " Segregation." We shall see 

 later on how this fact explains the phenomena 

 observed, and how owing to it the parental 

 characters are transferred (or not transferred) by 

 the offspring to the ne.xt generation in a definite 

 and regular manner. In this re-sortment (segre- 

 gation) each character behaves as a unit and is 

 present as a wliole in the gamete formed or 

 totally absent from it. If the characters are 

 opposite in nature, as rose and single comb, only 

 one of them can be present in the gamete. Such 

 characters are said to be allelomorpliic, i.e., one or 

 the other only can be present in anygamete. Thus 

 the gamete of an impure or cross-bred bird will be 

 pure for the character it contains, and the cross- 

 bred individual gives rise to two different kinds 

 of gametes, e.g., an impure rose-comb bird forms 

 gametes, some of which contain roseness only. 



