THE PROBLEMS IN MATING AND IN EGG PRODUCTION 125 



detail to show the nature of Mendel's discovery of the law of 

 Gametic Segregation. 



It is one of the most marvellous of the discoveries of science 

 that by means of this law the breeder is able to predict before- 

 hand the result of mating his stock. He may take a pair of 

 these cross-bred fowls, both white plumage and rose-combs, 

 and knowing their pedigree, i.e., their gametic heritage, can 

 tell the number of rose-combs and single-combs of white 

 plumage or black plumage which he will get. The gain to 

 the breeder is enormous. Although the parents were hetero- 

 zygous {i.e. in common parlance mongrels), he gets four birds 

 out of the sixteen, one-fourth of the group, which will breed 

 true, viz., the rose-combed white (WWRR), the single-combed 

 white (WWss), the rose-combed black (bbRR), and the single- 

 combed black (bbss), and that of these four two of them, the 

 (WWRR) and the (bbss), are new forms, new varieties, proof 

 of the theory of Discontinuous Variation. These are marked 

 with an * in the tabulated list. 



Mendel's Theory Summarized. — "Mendel discovered an im- 

 portant set of facts, and he also suggested a theoretical interpre- 

 tation — the theory of gametic segregation. As Mr. Bateson 

 says: 'The essential part of the discovery is the evidence 

 that the germ-cells or gametes produced by cross-bred or- 

 ganisms may in respect of given characters be of the pure; 

 paternal type, and consequently incapable of transmitting 

 the opposite character; that when such pure similar gametes 

 of opposite sexes are united in fertilization, the individuals so 

 formed and their posterity are free from all taint of the cross ; 

 that there may be, in short, perfect or almost perfect discon- 

 tinuity between these germs in respect of one of each pair of 

 opposite characters' " (Professor Thompson, Heredity, p. 

 347). 



"The essential feature of Mendel's discovery is the segrega- 

 tion in the gametes of the factors corresponding to the 

 dominant and the recessive characters" (R. C. Pimnett, Men- 

 delism, p. 30). 



"The breeding pen is to us what the test tube is to the chem- 

 ist, an instrument whereby we examine the nabure of our 

 organisms and determine their genetic properties" (Bateson). 



