THE MECHANICS OF MUTATION 



M7 



This will unite with an unchanged velans gamete to give a ring of 

 six and four pairs, as follows : 



velans {A^B Cfi E^F [G.H {KJ. {M^N (OP 



\/ \/ \ 



subvelans Bf Dfi F^A) G^H) K^L) M^.N) OP) 



Fig. 107. — Left, three metaphase configurations derived from 

 Fig. 106 (2) ; chiasma formation in the interstitial segment 

 gives chromatid non-disjunction always. Right, metaphase 

 configurations derived from Fig. 106 (3). Below, chiasma . 

 formation in the differential may give chromatid non-disjunction 

 of the cross-over or of the old chromatids. (D., 1936 a.) 



Such is the configuration found in the so-called " half-mutant " 

 rubrinervts, which appears in the selfed progeny of CEnothera 

 Lamarckiana once in a thousand seedlings. 



Moreover, it will be seen that the mutant, on this hypothesis 



