HETEROZYGOTE FORMS 193 



Both these forms, then, the black and the splashed 

 white, are clearly pure homozygotes. On mating a 

 black and a splashed white together, black-bearing 

 gametes and white-bearing gametes will meet together 

 in fertilization. In every case in which this form of 

 mating was carried out the resulting chicks were 

 invariably blue. 



The gametes of the blue type of Andalusians, then, 

 according to our supposition, do not bear the blue 

 character at all. Half of them contain the black and 

 half of them the splashed white allelomorph. Such 

 gametes, meeting by chance when a pair of blue An- 

 dalusians are mated together, give rise to the zygotes 

 one black-black, two black-white, one white-white 

 the black-whites being, of course, blue in appearance 

 as before* 



Now, we may put this explanation to the test by a 

 very simple experiment namely, by mating the sup- 

 posed heterozygote blues with the black and with 

 the splashed white types respectively. Both these 

 forms of mating were examined by Bateson and 

 Punnett, and the results were as follows ; It was found 

 that blues crossed with blacks gave rise to equal 

 numbers of blue and of black offspring, whilst when 

 blues were crossed with splashed whites there ap- 

 peared blue and splashed white chicks in equal numbers. 

 And by a repetition of the process it could be shown 

 that the blues so obtained were heterozygotes as before. 

 Here, then, we have clear evidence that equal numbers 

 of the germ-cells produced by the blue birds bear the 

 pure black allelomorph and the pure splashed white 



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