Owing to the excellent viability and the perfect sharpness of separation, white was extensively used in linkage experiments, especially with miniature and yellow (Morgan, 1911a; Morgan and Cattell, 1912 and 1913). White has been more extensively used than any other character in Drosophila, though it is now being used very little because of the fact that the double recessives of white with other sex-linked eye-colors, such as vermilion, are white, and consequently a separation into the true genetic classes is impossible. The place of white has been taken by eosin, which is an allelomorph of white and which can be readily used with any other eye-color.
The locus of white and its allelomorphs is only 1.1 units from that of yellow, which is the zero of the chromosome. Yellow and white are very closely linked, therefore giving only about one cross-over per 100 flies.
All the published data upon the linkage of white with other sex-linked characters have been collected into table 65.
RUDIMENTARY.
Rudimentary, which appeared in June 1910, was the second sex-linked character in Drosophila (Morgan, 1910c). Its viability has always been very poor; in this respect it is one of the very poorest of the sex-linked characters. The early linkage data (Morgan, 1911a) derived from mass cultures have all been discarded. By breeding from a single F1 female in each large culture bottle it has been possible to obtain results which are fairly trustworthy (Morgan, 1912g; Morgan and Tice, 1914). These data appear in table 65, which summarizes all the published data.
The locus of rudimentary is at 55.1, for a long time the extreme right end of the known chromosome, though recently several mutants have been found to lie somewhat beyond it.
The rudimentary males are perfectly fertile, but the rudimentary females rarely produce any offspring at all, and then only a very few. The reason for this is that most of the germ-cells cease their development in the early growth stage of the eggs (Morgan, 1915a).
MINIATURE.