48 THE UNIVERSITY OF OKLAHOMA 



acquire a certain special development of a particular part. So 

 that instead of uniformity of values for the mitotic index we get 

 a i^reat variety. But nevertheless there is a general decline." 



XXII. SOMATIC MUTATIONS AND ELYTRAL MOSAICS 



IN BRUCHUS 



J. K. Breitenbecher. 



From the Zdological Laboratory of the University of Oklahoma. 

 Contribut'on No. 19, Second Series. 



During the years 1918-1921 thirty-one unusual females were dis- 

 covered during the progress of our work upon the genetics of 

 Bruchus quadriniaculatiis. The most striking feature about these 

 insects was the fact that the elytra were of different colors. ThcM- 

 differences are therefore elytral mosaics, and the fact that no 

 mosaic was transmitted when mated with normal individuals indi- 

 cates that these are caused by somatic mutations. 



Since these mosaics originated from cultures used for a detailed 

 study of a multiple allelomorph series, it seems desirable to con- 

 sider the normal homozygous insects for each mutant tested. The 

 unsual expectancy for homozygous cultures is that the elytra of 

 the normal female v^'ill be red-red for the red mutant stock, black- 

 black for the black one, white-white for the white mutant, and tan- 

 tan for the wild type. But in these thirty-one cases, types of mosaic 

 elytra have appeared such as red-black, black-red, tan-black, black- 

 tan , white-black, etc. 



It is easier to interpret these mosaics if one describes them in 

 the order of their dominances (red, black, white, and tan or wild 

 type). No mosaics were discovered in any pure culture for red, 

 because they would all be recessives and could not be seen. Twelve 

 l)lack-red and eight red-black mosaics originated from homozygou.'' 

 black cutures because red is a somatic dominant to black. One 

 black-white mosaic was found in a pure culture for v/hite ; here 

 black is dominant to white. The wild tocks produced eight mosaics 

 in all : six had tan-black elytra, one black-tan elytra, and the last 

 one white-tan elytra. It is evident that the appearance of a mosiac 

 was visible because it was dominant to the body and elytra color 

 for which the culture was pure. 



Discussion 



These somatic modifications in Bruchus are not due to factor 

 mutations in the germ cells, because they are not transmitted. The 

 obvious conclusion is that these elytra mosiacs are due to somatic 

 mtitations The evidence indicates that these somatic mutations are 



