64 



HEREDITY 



ought to happen if we cross a pure " disguised grey " 

 with a pure breeding black type ? The factor C is 

 introduced by the black parent, the factor G through 

 the wliite, so that the first generation should all be grey. 

 This supposition has been tested, and is what actually 

 occurs. The production of grey offspring by a black 

 and a white parent is another case of reversion, brought 

 about by recombination of characters on crossing. 



A different type of inheritance may be exemphfied 

 by the case of black colom* in the glumes or hulls of oats, 

 discovered by the Swedish investigator Nilsson-Elile. 

 Three types exist — wliite, greyish-black, and deep black. 

 A cross between grey-black and white gives grey-black 



Fig. 10. 



hybrids, with normal segregation in the next genera- 

 tion into 3 grey-black : 1 white. Similarly, black and 

 grey-black give black, with normal segregation into 

 3 black : 1 grey-black. A cross between black and white 

 gives black in the first generation, but in the following 

 generation the ratio obtained is not that of 3 black : 

 1 white, but is 9 black ; 6 grey-black ; 1 white. The 

 explanation of this is that the black colour is produced 

 by the simultaneous action of two independent factors. 

 Either of these alone produces grey-black, and when 

 both are absent the colour is white. The 9:6:1 

 ratio is therefore only a special case of the 9:3:3:1 

 ratio that we already know. 



