20 LES5ON5 IN POULTRY KEEPING SECOND 5ERIE5. 



As preliminary to a correct understanding of the scope of the investigations of Mendel, and 

 of the possible application of bis law in poultry breeding, it is necessary to understand that 

 the greater number of Mendel's experiments in crossing were made with peas, and that his* 

 observations were In most cases confined either to noting the results with respect to reproduc- 

 tion of a particular character from a union of specimens differing in that character. Thus, he 

 would cross a tall and a low variety of peas, and observe and classify resulting plants accord- 

 Ing to height. He would cross a variety having the seed round and smooth when ripe with one 

 having wrinkled seed, and note the character of the seed from the resulting plants. And so on 

 through a variety of minor differences. In a few cases he made comparisons for two pairs of 

 characters, and found that the mathematical proportion discovered for the single pair was still 

 maintained, but there was nothing in his work at all approaching in complexity the task of the 

 poultry breeder who might undertake to make au application of Mendel's law to such number 

 and variety of characters as we have in fowls. 



Anything like a general application of Mendel's law to the phenomena of poultry breeding is 

 at present out of the question. Indeed, though a mathematician might find mathematical 

 expression for the application of the law to many varying characters, it would be practically 

 impossible to separate the offspring of a mating made with such an end in view, and to identify 

 the fowls equivalent to the factors in the mathematical statement. For the present and per- 

 haps for all time poultrymen must work with Mendel's law as he worked with it, applying it 

 to but one or two characters at a time. 



However it may seem to those not versed in the histories of breeds and varieties, to experi- 

 enced breeders this limitation of the application of the law will not appear to diminish its 

 practical value. The experienced breeder knows none better how all but impossible it is 

 to make rapid advance in the development of more than one important feature at a time. What 

 the Mendel law gives promise of being able to do for the breeder of poultry is to help him to 

 make more rapid and more certain progress point by point. As Bateson puts it, Mendel's 

 " work relates to the course of heredity in cases where definite varieties differing from each. 

 other in some one definite character are crossed together. * * * It was found that in 

 each case the offspring of the cross exhibited the character of one of the parents in almost 

 undimlnished intensity, and intermediates which could not be at once referred to one or other 

 of the parental forms were not found. 



" In the case of each pair of characters there is thus one which in the first "cross prevail* to 

 the exclusion of the other. This prevailing character Mendel calls the dominant character, the 

 other being the recessive character. 



" That the existence of such ' dominant' and 'recessive' characters is a frequent phenome- 

 non in cross breeding, is well known to all who have attended to these subjects. 



"By letting the crossbreds fertilize themselves Mendel next raised another generation. In 

 this generation were individuals which showed the dominant character, but also individuals 

 which presented the recessive character. Such a fact also was known in a good many 

 instances. But Mendel discovered that in this generation the numerical proportion of domi- 

 nants to recessives is on an average of cases approximately constant, being in fact as three to 

 one. With very considerable regularity these numbers were approached in the case of each of 

 bis pairs of characters. 



"There are thus in the first generation raised from the crossbreds seventy-five per cent 

 dominants and twenty-five per cent recessives. 



"These plants were again self-fertilized, and the offspring of each plant separately sown. 

 It next appeared that the offspring of the recessives remained pure recessive, and in subsequent 

 generations never produced the dominant again. 



"But when the seeds obtained by self-fertilizing the dominants were examined and sown it 

 was found that the dominants were not all alike, but consisted of two classes: (1) those which 

 gave rise to pure dominants; and (2) others which gave a mixed offspring, composed partly 

 of recessives, partly of dominants. Here also it was found that the average numerical pro- 

 portions were constant, those with pure dominant offspring being to those with mixed offspring 

 as one to two. Hence it is seen that the seventy-five per cent dominants are not really of 

 .similar constitution, but consist of twenty-five which are pure dominants, and fifty which are 



