HEREDITY 



ring. Hence, also, we are forced to conclude, 

 as already suggested, the female of the pure 

 barred Rock breed is heterozygous as re- 

 gards barring, and transmits the character only 

 to her male offspring, her female offspring 

 (if the father is non-barred) neither being 

 themselves barred nor being able to transmit 

 barring. 



A pure Plymouth Eock race breeds true to 

 barring merely because all its males are pure, 

 for the females are not pure. This is shown 

 by the following experiment. If a heterozygous 

 barred male, produced by a cross between a 

 Eock and a non-barred breed, is crossed with 

 barred females, either those of a pure Eock 

 race or those produced by a cross, the result 

 is the same. The male offspring are all barred ; 

 the females, half of them barred, half non- 

 barred. This result shows that all barred 

 females alike are heterozygous in barring. 



Sex-limited inheritance such as this finds at 

 the present time its most probable explanation 

 in the existence in the egg of an extra or plus 

 element never found in the sperm, this element 

 pairing with the sex-limited character in the 



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