Linkage Data. 41 



mate, but they are probably reliable to the extent of indicating that 

 the serial order of the genes is scaly-hunch-telescoped and in showing 

 that hunch and telescoped are more closely linked than are scaly 

 and hunch. The former value is probably reasonably accurate. 



Scaly, hunch, telescoped, and garnet. — The relative "location" 

 of garnet was determined by a back-cross involving garnet on one 

 side and scaly hunch telescoped on the other. This is summarized 

 in experiment 61. It gives garnet a position on the opposite end 

 of the map from scaly. The numbers are not large enough to give 

 accurate cross-over data, but they support the preceding experiment 

 in indicating that the loci of hunch and telescoped are relatively 

 close together, while that of scaly is remote from both. That of 

 garnet is likewise remote, but in the opposite direction. As indicated 

 by the table, two sets of values may be considered, one based on the 

 total count and the other on only the flies showing scaly. In either 

 case the telescoped-garnet value is so large as to indicate that these 

 two loci are probably 50 or more units apart. As a result of the 

 remoteness of scaly and garnet from the other two loci, double 

 crossing-over is high. In fact the single cross-overs in region 2 

 are not as numerous as either type of doubles involving this region. 

 Even the triples appear to exceed this class of singles, but this is 

 probably due in part to the failure of scaly to appear in some of the 

 flies classified as hunch. Taken at their face value, the data suggest 

 that hunch and telescoped may be in the reverse order from that 

 given. This should be kept in mind as a possibility, although it is 

 opposed by the more extensive data from experiment GO, which are 

 the ones used here for the tentative determination of serial order. 



Spread and garnet. — Two back-crosses involving these two genes 

 (in opposite chromosomes) gave 59 cross-over flies and 82 non-cross- 

 overs. This gives a cross-over value of 41.8 per cent (experiment 59), 

 indicating that spread is remote from garnet, thus agreeing with the 

 experiment involving scaly and spread, which placed spread near 

 the zero end of the map. 



CONSTRUCTION OF THE THIRD-CHROMOSOIVIE MAP. 



(Figure 7.) 



The data available for constructing a map of the third chromosome 

 are given in tables 5 and 6. For reasons given above, only a rough 

 map can be constructed at present. In table 5 the data are arranged 

 according to experiments, w^hile in table 6 they are arranged according 

 to the map regions involved. In both tables two sets of values are 

 given for some of the experiments. The upper value in these cases 

 is based on all of the flies, and the lower value on only those showing 

 scaly. In the experiment involving scaly and hunch alone the two 

 values, thus obtained, differ markedly. But the numbers are small 



