Table 56.—Summary of linkage data on lethal 3, from Morgan, 1914c.
| Gens. | Total. | Cross- overs. | Cross-over values. |
| Eosin lethal 3 | 1,327 | 268 | 20.2 |
| Eosin vermilion | 1,327 | 357 | 27.0 |
| Eosin miniature | 3,374 | 967 | 29.0 |
| Club lethal 3 | 222 | 29 | 13.0 |
| Club vermilion | 877 | 161 | 18.4 |
| Lethal 3 vermilion | 1,549 | 105 | 6.8 |
| Lethal 3 miniature | 1,481 | 138 | 9.3 |
| Vermilion miniature | 1,327 | 31 | 2.3 |
LETHAL 3a.
In January 1914 a vermilion female from a lethal 3 culture when bred to a vermilion male gave 71 daughters and only 3 sons; 34 of these daughters were tested, and every one of them gave a 2:1 sex-ratio. The explanation advanced (Morgan 1914c) was that the mother of the high ratio was heterozygous for lethal 3, and also for another lethal that had arisen by mutation in the X chromosome brought in by the sperm. On this interpretation the few males that survived were those that had arisen through crossing-over. The rarity of the sons shows that the two lethals were in loci near together, although here of course in different chromosomes, except when one of them crossed over to the other. As explained in the section on lethal 1 and 1a the distance between the two lethals can be found by taking twice the number of the surviving males (2+3) as the cross-overs and the number of the females as the non-cross-overs. But the 34 daughters tested were also non-cross-overs, since none of them failed to carry a lethal. The fractions (6+0)/(71+34) = 6/105 give 5.7 as the distance between the lethals in question. In the case of lethals 3 and 3a another test was applied which showed graphically that two lethals were present. Each of the daughters tested showed, by the classes of her sons, the amount of crossing-over between white and that lethal of the two that she carried. These cross-over values were plotted and gave a bimodal curve with modes 7 units apart. It had already been shown that the locus of one of the two lethals was at 26.5, and since the higher of the two modes was at about 23, it corresponds to lethal 3. The data and the curve show that the lethals 3 and 3a are about 7 units apart, i. e., lethal 3a lies at about 19.5.
LETHAL 1b.
A cross between yellow white males and abnormal abdomen females gave (February 1914) regular results in 10 F2 cultures, but three cultures gave 2 ♀ : 1 ♂ sex-ratios (Morgan, 1914b, p. 92). The yellow white class, which was a non-cross-over class in these 10 cultures, had disappeared in the 3 cultures. Subsequent work gave the data summarized in table 57. At the time when the results of table 57 were obtained it did not seem possible that two different lethals could be present in the space of about 1 unit between yellow and white, and this lethal was thought to be a reappearance of lethal 1 (Morgan, 1912b, p. 92). Since then a large number of lethals have arisen, one of them less than 0.1 unit from yellow, and at least one other mutation has taken place between yellow and white, so that the supposition is now rather that the lethal in question was not lethal 1. Indeed, the linkage data show that this lethal, which may be called lethal 1b, lies extraordinarily close to white, for the distance from yellow was 0.8 unit and of white from yellow on the basis of the same data 0.8. There was also a total absence of cross-overs between lethal 1b and white in the total of 846 flies which could have shown such crossing-over. On the basis of this linkage data alone we should be obliged to locate lethal 1b at the point at which white itself is situated, namely, 1.1, but on a priori grounds it seems improbable that a lethal mutation has occurred at the same locus as the factor for white eye-color. Farther evidence against this supposition is that females that have one X chromosome with both yellow and white and the other X chromosome with yellow, lethal, and white are exactly like regular stock yellow white flies. The lethal must have appeared in a chromosome which was already carrying white and yet did not affect the character of the white. We prefer, therefore, to locate lethal 1b at 1.1-.
Table 57.—Summary of all linkage data upon lethal 1b, from Morgan, 1914b.
| Gens. | Total. | Cross- overs. | Cross-over values. |
| Yellow lethal 1b | 744 | 6 | 0.81 |
| Yellow white | 2,787 | 23 | 0.82 |
| Lethal 1b white | 846 | 0 | 0.0 |
FACET.