OF MUTANT CHARACTERS. 



303 



the zero-point and the others have consecutive numbers in a single 

 series. The map made in this way has already been given on page 127. 



In using such a map one should keep in mind both the locus as given 

 and the manner in which that locus 

 has been established, since this largely 

 determines not only the accuracy but 

 also the significance of any particular 

 location. 



A type of diagram which is capable 

 representing fully the relationship 



10 



; - 15.4 



zo 



fat- 



38.0 

 Z9.O 



40 



50 



60 



70 



80 



90 



- - 35.5 



-465 

 -46.7 



48.5 



50.0 



- - (62.5 



65.0 

 66.5 



- - 73.5 



of 



of each locus to the other loci is given 



in text-figure 87. 



This diagram could be further elab- 

 orated by making the heaviness of line 

 correspond to the accuracy of data, 

 and by giving, besides the final, the 

 reference-base positions. Thus pr vg 

 gives a locus of vestigial at 6+18.0, 

 while the corrected black vestigial data 

 indicate a locus of vestigial at 6+18.9, 

 while the locus actually given in the 

 diagram is the mean position for ves- 

 tigial at 18.5 



The type of map which is in daily use 

 in our laboratory is that given in text- 

 figure 88, in which the loci are further 

 classified according to the value of the 

 character, etc. Thus, the mutants of 

 first rank in value are made conspic- 

 uous and insured first consideration by 

 being lined up at the extreme left edge 

 of the space. The mutants nearly as 

 good, but whose usefulness is restricted 

 in one or another respect, are spaced 

 next in order. Still further to the right 

 are those whose loci are not well estab- 

 lished or whose characteristics are such 

 that they are useful only in experiments 

 of a very special nature. At the ex- 

 treme right are the mutants no longer 

 available, because the stocks have been 

 lost or discarded. This type of map can 

 be kept subject to continuous changes 

 in the valuations or the locations of the 

 different mutants by drawing the map-scale on a soft board and 

 mounting the symbols for each mutant on the head of a thumb-tack. 



100 



no 



96.2 

 -98.0 

 -98.4 



TEXT-FIGURE 88. Working and valua- 

 tion map of the second chromosome. 

 The loci mapped at the left margin rep- 

 resent the most valuable mutants, 

 those farther to the right progressively 

 less useful. Those next the right 

 margin are mutants no longer extant. 



