In order to determine the location of facet in the first chromosome, one of the facet males which appeared in culture 66 was crossed out to vermilion sable females. Three of the wild-type daughters were back-crossed to vermilion sable males. The females of the next generation should give data upon the linkage of vermilion and sable, while the males should show the linkage of all three gens, facet, vermilion, and sable. The offspring of these three females are classified in table 59. The cross-over fraction for vermilion sable as calculated from the females is 19/194. The cross-over value corresponding to this fraction is 10 units, which was the value found in the more extensive experiments given in the section on sable. It will be noticed that the results in the males of culture 150 are markedly different from those of the other two pairs. While the sable males are fully represented, their opposite classes, the gray males, are {77} entirely absent. This result is due to a lethal factor, lethal 5, which appeared in this culture for the first time. The males of the two cultures 149 and 151 give the order of gens as facet, vermilion, sable; that is, facet lies to the left of vermilion and toward yellow. The cross-over values are: facet vermilion 40; vermilion sable 12; facet sable 42. Since yellow and vermilion usually give but 34 per cent of crossing-over, this large value of 40 for facet vermilion shows that facet must lie very near to yellow. TABLE 59.--_P_1 facet_ [male] x _vermilion sable_ [female] [female]. _B.C. F_1 wild-type_ [female] x _vermilion sable_ [male] [male]. +----------+----------------------------------+ | | F_2 females. | | +----------------+-----------------+ | | | | | |Non-cross-overs.| Cross-overs. | | | | | |Reference.+---------+------+----------+------+ | |Vermilion|Wild- |Vermilion.|Sable.| | |sable. |type. | | ~ | | | | | ~ +----------+---------+------+----------+------+ | 149 | 16 | 29 | 3 | 3 | | 150 | 13 | 17 | 2 | 2 | | 151 | 37 | 63 | 7 | 2 | | +---------+------+----------+------+ | Total. | 66 | 109 | 12 | 8 | +----------+---------+------+----------+------+