of Heredity 23 



in those two forms or varieties need not give any indication 

 as to the character of the zygote A a. It may display the 

 character A, or , or a character halfway between the two, 

 or a character beyond A or below a. The character of A a 

 is not regarded as a heritage transmitted to it by A and by 

 , but as a character special and peculiar to Aa, just as 

 NaCl is not a body half way between sodium and chlorine, 

 or such that its properties can be predicted from or easily 

 stated in terms of theirs. 



If a concrete case may help, a tall pea A crossed with 

 a dwarf a often produces, not a plant having the height of 

 either A or a, but something taller than the pure tall 

 variety A. 



But if the case obeys the Mendelian principles as does 

 that here quoted then it can be declared first that the 

 gametes of Aa will not be bearers of the character proper to 

 Aa ; but, generally speaking, each gamete will either bear 

 the pure A character or the pure a character. There will 

 in fact be a redistribution of the characters brought in by 

 the gametes which united to form the zygote Aa, such that 

 each gamete of Aa is pure, as the parental gametes were. 

 Secondly this redistribution will occur in such a way that, 

 of the gametes produced by such Aa's, on an average 

 there will be equal numbers of A gametes and of a 

 gametes. 



Consequently if Aa's breed together, the new A gametes 

 may meet each other in fertilisation, forming a zygote A A, 

 namely, the pure A variety again ; similarly two a gametes 

 may meet and form aa, or the pure a variety again. But if 

 an A gamete meets an a it will once more form Aa, with 

 its special character. This Aa is the hybrid, or "mule" 

 form, or as I have elsewhere called it, the heterozygote, as 

 distinguished from A A or aa the homozygotes. 



