158 ANIMAL LIFE AM) HUMAN PKOGEESS 



far-reaching. It had been proved before Mendel's time that 

 the genesis of a fresh individual commenced with the fusion of 

 two germ cells, one from the male and one from the female 

 parent. The identities of these two germ cells, or gametes as 

 we now call them, were regarded as entirely merged in the 

 identity of the resulting individual, or zygote, which hence- 

 forth possessed a unit identity of its own. Mendel's discovery 

 has led us to regard the zygote as a compound or dual structure, 

 of which the exhibited characters are dependent sometimes 

 solely upon the one or the other of the two gametes of which it 

 is compounded. The process by which gametes arise from the 

 zygote is a process by which the duahty of the zygote is re- 

 solved as it were into its components, and the gametes so pro- 

 duced are again units capable of uniting with others to form 

 dual structures once more. 



If all the gametes are precisely ahke, zygotes resulting from 

 their various fusions will also be all aUke and we shall be 

 dealing with a uniform strain. A true-breeding race of Black 

 Rosecomb Bantams forms such a strain, and the White Eose- 

 combs form another. A pure black Rosecomb was formed 

 from two black gametes, and the dual structure which it 

 represents was formed of like components (Fig. 1). When, 

 therefore, the dual structure is resolved and gametes arise 

 from it these are all alike,i i.e. all black. So also the gametes 

 of the White Rosecombs are all white. Now what happens 

 when White and Black Rosecombs are mated together 1 

 Experiment has shown that the ofispring are all black. The 

 influence of the black is dominant. Nevertheless we know 

 from the form of the experiment that our dual structure here 

 is formed from unlike components, viz. one "black" gamete 

 and one " white " one. What is going to happen when such a 

 dual structure is resolved— when it itself gives rise to gametes ? 

 The answer to this question has been deduced from the results 

 of breeding such birds together (Fig. 2), and of crossing them 

 back with the parental strains (Fig. 3) . When mated together 

 they give blacks and whites in the ratio of 3 : 1 ; when crossed 



1 Excluding, of course, those differences upon which the manifestation 

 of sex depends. 



