ABNORMAL ABDOMEN.
([Plate I]. figure 4.)
The dominant sex-linked character abnormal abdomen appeared in July 1911 (Morgan, 1911d). It was soon found that the realization of the abnormal condition depended greatly upon the nature of the environment (Morgan, 1912). Recently a very extensive study of this character has been published (Morgan, 1915). As this case has been reviewed in the introduction, there is little further to be said here.
Because of the change that takes place as the culture grows older (the abnormal changing to normal), this character is not of much value in linkage work. The location of the factor in the X chromosome at 2.4 has been made out from the data given by Morgan (1915b). These data, which in general include only the abnormal classes, are summarized in table 1.
Table 1.—Linkage data, from Morgan, 1915b.
| Gens. | Total. | Cross- overs. | Cross-over values. |
| Yellow white | 28,018 | 334 | 1.2 |
| Yellow abnormal | 15,314 | 299 | 2.0 |
| White abnormal | 16,300 | 277 | 1.7 |
EOSIN.
([Plate II], figures 7 and 8.)
The recessive sex-linked mutation eosin eye-color appeared in August 1911 in a culture of white-eyed flies (Morgan 1912a). The eye-color is different in the male and female, the male being a light pinkish yellow, while the female is a rather dark yellowish pink. Eosin is allelomorphic to white and the white-eosin compound or heterozygote has the color of the eosin male. There is probably no special significance in this coincidence of color, since similar dilutions to various degrees have been demonstrated for all the other eye-colors tested (Morgan and Bridges, 1913). Since eosin is allelomorphic to white, its locus is also at 1.1. Eosin is the most useful character among all those in the left end of the chromosome.
BIFID.