MENDEL'S SECOND LAW 



61 



to save space and time. It is customary to represent 

 the members of a pair by the same letter, as Mendel 

 himself did, and to represent the dominant member by 

 the capital letter, the recessive member by a small letter. 

 Thus if ^ = tall and a = short; and 5=^ color and 

 & = white, the recombination square becomes: 



Eggs AB 



Sperm 

 AB 



Ab 

 aB 

 ab 



Ab 



aB 



ab 



Instead of using arbitrary letters for the characters 

 as above, it has been found more convenient to use a 

 mnemonic system in which the first letter of one of the 

 members of each pair becomes the symbol. The two 

 members of such a pair are then distinguished from each 

 other by using a capital letter for one and a correspond- 

 ing small letter for the other. For example, we might 

 let t = short, T = tall, c = white, C = color. In this 

 case the capital letter represents the dominant character, 

 and the small letter represents the loss of that character, 

 as seen in the recessive type. But besides prejudging the 

 question as to what kind of a change took place in the 

 germ-plasm to change a dominant to a recessive by 

 assuming that it is due to a loss, this system is unsatis- 

 factory in cases where many modifications of the same 

 organ exist (such as the 40 eye colors of the vinegar fly), 



