104 MENDELISM CHAP. 



male. The FI female, owing to the repulsion between 

 F and G, produces only the two kinds of ova Fg and 

 /G, and produces them in equal numbers. Since 

 the lacticolor male can contain neither F nor G, all 

 of its spermatozoa must be fg. The results of such 

 a cross, therefore, should be to produce equal num- 

 bers of the two kinds of zygote Ffgg and ffGg, i.e. 

 of lacticolor females and of grossulariata males. And 

 this, as we have already seen, is the actual result 

 of such a cross. 



Before leaving the currant moth we may allude to an 

 interesting discovery which arose out of these experi- 

 ments. The lacticolor variety in Great Britain is a south- 

 ern form and is not known to occur in Scotland. Matings 

 were made between wild Scotch females and lacticolor 

 males. The families resulting from such matings were 

 precisely the same as those from lacticolor males and FI 

 females, viz. .grossulariata males and lacticolor females 

 only. We are, therefore, forced to regard the constitution 

 of the wild grossulariata female as identical with that of 

 the FI female, i.e. as heterozygous for the grossulariata 

 factor as well as for the factor for femaleness. Though 

 from a region where lacticolor is unknown, the "pure" 

 wild grossulariata female is nevertheless a permanent 

 mongrel, but it can never reveal its true colours unless it is 

 mated with a male which is either heterozygous for G or 

 pure lacticolor. And as all the wild northern males are 



