+---------------------------------------------------------+ | Second generation. | +-------------------+-------------------------------------+ | w^c d_p | w^c | w^c d_p v | | --+----- | -----+-- | --+----+--- | | v | d_p v | | +---------+---------+--------+---------+---------+--------| ~ | | | | | | ~ Cherry | | Cherry |Depressed|Cherry | Wild- | |depressed|Vermilion| |vermilion|depressed| type | | | | | |vermilion| | | [male]. |[male]. |[male]. | [male]. | [male]. | [male].| +---------+---------+--------+---------+---------+--------+ | 6 | 6 | 5 | 5 | 0 | 0 | +---------+---------+--------+---------+---------+--------+
In May 1913 there were observed in a certain stock some flies which, although mature, did not unfold their wings (text-fig. H_a_). This condition was at first found only in males and suspicion was aroused that the character might be sex-linked. When these males were bred to wild females the club-shaped wings reappeared only in the F_2 males, but in smaller number than expected for a recessive sex-linked character. The result led to the further suspicion that not all those individuals that are genetically club show club somatically. These points are best illustrated and proven by the following history of the stock:
[Illustration: FIG. H.--Club wing. _a_ shows the unexpanded wings of club flies; _c_ shows the absence of the two large bristles from the side of the thorax present in the normal condition of the wild, b.]
Club females were obtained by breeding F_2 club males to their F_2 long-winged sisters, half of which should be heterozygous for club. { 69} 5,352; wild-type [male], 4,181; club [male], 236. The wild-type males include, of course, those club males that have expanded wings (potential clubs).
Club females by wild males gave in the F_2 generation (mass cultures): wild-type [female], 1,131; wild-type [male], 897; club [female], 57; club [male], 131.
It is noticeable that there were fewer club females than club males, equality being expected, which might appear to indicate that the club condition is more often realized by the male than by the female, but later crosses show that the difference here is not a constant feature of the cross.
Long-winged males from club stock (potential clubs) bred to wild females gave in F_2 the following: wild-type [female], 521; wild-type (and potential club) [male], 403; club [male], 82.