No. 614] THE BLUE ANDALUSIAN 



L09 



F 2 lErEr = black + 2 Er eR = blue + 1 eR eR = blue- 

 splashed. 



The gametes produced by the Fj (blues) are Er and efl. 

 If crossing-over should occur there would be occasional 

 ER and er gametes produced. It is highly interesting to 

 note that if these two classes of cross-over gametes were 

 produced in equal numbers, as would be expected, and the 

 individuals producing them were mated with ordinary 

 blues, exactly the same phenotypic ratio would result as 

 from the unions of the non-cross-over gametes, viz. : 



F! crossover gametes Ordinary gametes of F 1 blue 



ER, er Er, eR 



F 2 ER Er = blue, ER eR = blue, er Er= black, er eR 

 = blue-splashed. 

 This is the usual ratio of 1 black to 2 blues to 1 blue- 

 splashed and would, from the very nature of the case, 

 escape observation as involving crossing-over unless care- 

 ful analysis were made of the hereditary constitution of 

 these particular F 2 individuals. 



Such analyses would not be impossible, though they 

 might be long and tedious. The matings which would un- 

 cover any of the cross-over types, if offspring were pro- 

 duced in sufficient numbers to make it fairly certain that 

 one were not dealing with chance variations in the ratios, 

 are given herewith. 



Cross-over blue of ER Er constitution mated with an 

 ordinary blue would give the following expectation : 



ER Er = blue cross-over X Er eR = ordinary blue ; 

 F, ER Er = blue, 



ER eR = blue, 

 ErEr = black, 

 EreR = b\ue, 



or 3 blues to 1 black, while the ordinary blues would give 

 the normal 1 black to 2 blues to 1 blue-splashed. 



Similarly this same individual mated with ordinary 

 blue-splashed would produce all blues instead of the ordi- 

 nary expectation of 1 blue to 1 blue-splashed, viz. : 



