BASES or CHANGli 



distinguishes all agouti from all non-agouti or all dark-bellies 

 from all light-bellies. Fisher has suggested that an inversion is 

 associated with the agouti difference (Fig. 26) and is putting this 

 view to an experimental test. 



AGOUTI LIGHT BELLY 

 H j-H ^ 



-O Wild type, U.S.A. 



AGOUTI 



dark belly 

 -HH -—& 



-OVVild type. G.B. 



non-agouti LIGHT BELLY 



{ O ^^o^ £ tan 



non-agouti dark belly 



~ 1 L -L .1 U L. U I I . 1 -L _ I " ■ I 1 ' ! " ■ "" — ■-- I' 



-OAII black 



i INVERSION / - 



LIGHT BELLY non-aqouti 



I-H h 



non-aqouti 

 H Z Y 



dark belly 



-X Black I tan 

 -X All black 



DEF/CIENCY 



Yellow 



Fig. 26. — The possible rcLition of structural changes to gene recombination in the 

 Agouti scries of the mouse, where four allelomorphs represent all recombinations 

 of two ditferences between which recombuiation has not, however, been observed. 

 The differences could be interpreted as two gene ditferences so closely linked as 

 never to recombine (two-gene system). Or one of them could be regarded as 

 associated with an inversion inhibiting recombination (one super-gene system). 



Further, it might be that what behave as two units of action under 

 one set ot external conditions, or in one set of internal relations, 

 behave as one unit of action under others. Indeed the position-effect 

 has already shown us this in another way. Finally, it seems that 

 recombination may be mistaken for mutation if it is rare enough. 

 This we have seen already at the Bar locus and wc shall see it again 

 in Oenothera. 



iS 



