In September 1912 a certain wild female produced 78 daughters and only 16 sons (Morgan, 1914_b_); 63 of these daughters were tested and 31 of them gave 2 females to 1 male, while 32 of them gave 1:1 sex-ratios. This shows that the mother of the original high sex-ratio was heterozygous for a recessive sex-linked lethal. In order to determine the position of this lethal, a lethal-bearing female was bred to an eosin (or white) miniature male, and those daughters that were heterozygous for eosin, lethal, and miniature were then back-crossed to { 50} eosin miniature males. The daughters that result from such a cross give only the amount of crossing-over between eosin and miniature (as 29.7), but the males give the cross-over values for eosin lethal (9.9), lethal miniature (15.4), and eosin miniature (25.1). The data for this cross are given in table 25.
TABLE 25.--_Total data upon linkage of eosin, lethal 2, and miniature, from Morgan, 1914b._
+------------------------------------+ | Females. | +--------+--------------+------------+ | | | | | Total. | Cross-overs. | Cross-over | | | | value. ~ | | | ~ +--------+--------------+------------+ | 15,904 | 4,736 | 29.7 | +--------+--------------+------------+
+-----------------------------------------------------------------------+ | Males. | +--------+--------+--------+---------+----------------------------------+ |w^e m|w^e l_2 |w^e |w^e l_2 m| Cross-over values. | |--------|---+----|------+-|---+---+-+----------+-----------+-----------+ ~ l_2 | m| l_2 m| | Eosin | Lethal 2 | Eosin | ~ | | | | lethal 2.| miniature.| miniature.| +--------+--------+--------+---------+----------+-----------+-----------+ | 5,045 | 653 | 1,040 | 14 | 9.9 | 15.4 | 25.1 | +--------+--------+--------+---------+----------+-----------+-----------+
A similar experiment, in which eosin and vermilion were used instead of eosin and miniature, is summarized in table 26.
TABLE 26.--_Total data upon the linkage of eosin, lethal 2, and vermilion, from Morgan, 1914b._
+------------------------------------+ | Females. | +--------+--------------+------------+ | | | | | Total. | Cross-overs. | Cross-over | | | | value. ~ | | | ~ +--------+--------------+------------+ | 2,656 | 729 | 27.5 | +--------+--------------+------------+