386 



PERMANENT HYBRIDS 



XYYcf 



XXX(3n)9 MC(3n) //r//'Af«=cf 



X0{5n)su/?^r.(^ y^Xsuper.^ XXX 9 ]&'XX'9 



XX' x" cf jiiA7jr//y/75.d' Ji[/v7//'j/75.d' ]ir/»ir//-^/75.9 



Fig. 121. — Diagram showing normal (A and B) and variant (C to P) 

 chromosome complements of Drosophila melano paster. Compiled 

 from Bridges, 1916 (D, E, F), 1922 (G, H, l/j), 1927 (A, B), 

 L. V. Morgan, 1922 (K), Stern, 1929 (L,' M — alternative sex- 

 mechanism), Painter and Muller, 1929 (N, O), and Dobzhansky, 

 1929 (P). Constrictions are emphasised. X ca. 9000. 



D, E and K the products of primary non-disjunction. F of 

 secondary non-disjunction. K of fusion. N, O, P of trans- 

 location. L and M of deletion with fusion. The structure of the 

 chromosomes is otherwise constant. The XO male and the 

 super-male and super-female forms are sterile, the first for 

 mechanical reasons, the others for physiological reasons. 



seen is the case, X having a resultant normal female effect, Y having 

 a neutral effect. Further, both must be internally balanced. In the 



