24 SEX-LINKED INHERITANCE IN DROSOPHILA. 



NOMENCLATURE. 



The system of symbols used in the diagrams and table headings is 

 as follows: The factor or gen for a recessive mutant character is 

 represented by a lower-case letter, as v for vermilion and m for mini- 

 ature. The symbols for the dominant mutant characters bar, abnormal, 

 and notch are B', A', and N'. There are now so many characters that 

 it is impossible to represent all of them by a single letter. We there- 

 fore add a subletter in such cases, as bifid (bi), fused (fu), and lethal 2 

 (I2). In the case of multiple allelomorphs we usually use as the base 

 of the symbol the symbol of that member of the system which was first 

 found and add a letter as an exponent to indicate the particular 

 member, as y"" for spot, w'' for eosin, and w" for cherry. The normal 

 allelomorphs of the mutant gens are indicated by the converse letter, 

 as V for not-vermilion, Bi for not-bifid, and b' for not-bar. In the 

 table headings the normal allelomorphs are indicated by position alone 



w^ B' 

 without the use of a symbol. Thus the symbol 



indicates that the female in question carried eosin, not-vermilion, and 

 bar in one chromosome and not-eosin, vermilion, and not-bar in the 



w^ V 



other. The symbol 1 d7 when used in the heading 



of a column in a table indicates that the flies classified under this 

 heading are the result of single crossing-over between eosin and ver- 



... . . . w^ B' 



mihon m a mother which was of the composition ; 



the symbol tells at the same time that the flies that result from a 

 single cross-over between eosin and vermilion in the mother are of the 

 two contrary classes, eosin bar and vermilion. When a fly shows two 

 or more non-allelomorphic characters the names are written from left 

 to right in the order of their positions from the zero end of the map. 



