Heredity and Sex 73 



are inA'ariablv mal es, the non-barred ones being females. 

 Accordingly, the distribution of barring and non-barring 

 in the cross is sex limited. 



The barred offspring produced by a cross between 

 barred Plymouth Rocks and a non-barred breed, whether 

 those offspring are males or females, prove to be heterozy- 

 gous in barring, as we should expect, the barring factor 

 having been received only from one parent, the barred one. 

 Further, the non-barred offspring produced by a barred. 

 Rock female crossed with a non-barred_breed, do not trans- 



mit barring, hence they are pure recessives as regards 

 barrmg. Hence, also, we are forced to conclude, as already 

 suggested, t he female of the pure barred Roc k breedj 

 heterozygou s as regards barring, and transm its the chara 

 onl y to her male offspring, her fem ale offs pring Uf the 

 faJher is non- barred), neither being themselves bj^d nor 

 Taeing able to transmit TSarring. 



A puxeLJElxm outh Rock race breeds truyjo^_j3.arring 

 merelv because all its males are _pure, for JJ^ females are 

 not pure^ This is shown by theT:ollo«ig experiment. 

 If a heterozygous barred male, produced^' a cross between 

 a Rock and a non-barred breed, is^rossed with barred 

 females, either those of a pure Roc^^ce or those produced 

 by a cross, the result is the same^^The male offspring are 

 all barred; the females, hal^^ them barred, half non- 

 barred. This result shows tWK all barred females alike 

 are heterozygous in barring. 



Sex-limite d inherita n ce such as this finds at the present , 

 time its mo st probable explanation in the existence in th ef 

 egg of an extra o r plns ^emeQt_m\ex ioxmd in the_spaiip7 \ 

 this element pairing with the sex-limited character in the 

 reduction division. Thus, in the barred Rock, calling 



