+----------+----------+----------------+---------------+--------+-------+ | | | Non-cross-over | Cross-over | | | | |Wild-type | [male] [male]. | [male] [male].| Total |Cross- | |Reference.|[female] +--------+-------+-------+-------+ [male] | over | | |[female]. | Ver- |Wild- | Ver- |Forked.| [male].|values.| | | | milion |type. |milion.| | | | | | | forked.| | | | | | +----------+----------+--------+-------+-------+-------+--------+-------+ | 9 I | 366 | 113 | 123 | 49 | 41 | 326 | 28 | | 11 I | 376 | 116 | 150 | 42 | 31 | 339 | 22 | | +----------+--------+-------+-------+-------+--------+-------+ | Total.| 742 | 229 | 273 | 91 | 72 | 665 | 25 | +----------+----------+--------+-------+-------+-------+--------+-------+ In table 39 vermilion forked and wild-type are non-cross-overs, and vermilion and forked are cross-overs, giving a cross-over value of 25 units. The locus, therefore, is 25 units to the right or to the left of vermilion, that is, either about 58 or 8 units from the yellow locus. LINKAGE OF CHERRY AND FORKED. Forked males were crossed to cherry females (cherry has the same locus as white, which is about 1 unit from yellow) and gave wild-type females and cherry males. These gave in F_2 the results shown in table 40. The non-cross-overs (cherry and forked) plus the cross-overs (cherry forked and wild type) divided into the cross-overs give a cross-over value of 46 units, which shows that the locus lies to the right of vermilion, because if it had been to the left, the value would have been 8 (_i. e._, 33-25) instead of 33+25=58. The difference between 58 {59} and 46 is due to the expected amount of double crossing-over. In fact, for a distance as long as 58 an almost independent behavior of linked gens is to be expected. TABLE 40.--_P_{1} cherry_ [female] [female] x _forked_ [male] [male]. _F_{1} wild-type_ [female] [female] x _F_{1} cherry_ [male] [male].