Gynandromorphs 497 



in the yolk in the center of a large egg and is surrounded by 

 some cytoplasm. It divides into two nuclei, each of which lies 

 in the yolk mass and is also surrounded by some cytoplasm. 

 These then divide into a number of nuclei with cytoplasm, all 

 lying within the yolk towards the center of the egg. Thus early 

 embryology in insects is very difTerent from that of other ani- 

 mals, but even if the early development were the same in all 

 animals it is possible that in insects the effect of abnormalities 

 during cleavage might be lost subsequently at metamorphosis. 

 A sharp median separation often appears in insects, but it is the 

 result of synchronous growth of the imaginal discs rather than 

 of cleavage. In Habrobracon, on the other hand, very few 

 gynanders and other mosaics are divided into male and female 

 halves with the boundary the midventral line; most are more or 

 less scrambled, several very much so. 



Individuals with both genetically male and female tissues are 

 called gynandromorphs or gynanders. Gynandromorphs differ 

 from intersexes. Intersexes are genetically alike throughout their 

 bodies ; on the contrary, however, gynandromorphs consist of two 

 genetically different kinds of tissue. Some cells are genetically 

 male and other cells are genetically female. 



Gynandromorphs have been found in Drosophila melanogaster, 

 in which one side of the body is male and the other female, and 

 the interpretation that has been given assumes that the male 

 side has lost one of the X chromosomes. If the fly is heterozy- 

 gous for a number of genes on the X chromosome, the female 

 side of the gynander will be phenotypically the expression of 

 all the dominant genes on both chromosomes. The male side, 

 however, will be the expression of either the dominants and re- 

 cessives on one or the other X chromosome, depending upon 

 which is lost. In so far as the genes on the autosomes are con- 

 cerned, the fly will be identical on both sides of its body. 



This gynandromorphic condition may theoretically result from 

 a complete loss of one X chromosome from a somatic cell, with 

 the result that all the cells that arise from this cell or from 

 its descendants will lack one X chromosome and will be XO, 

 whereas the remainder of the body will be XX. Such a loss could 

 result from an abnormal mitosis in which probably one of the 

 X chromosomes failed to be included in a daughter nucleus and 

 became embedded in the cytoplasm, where it degenerated. On 



