GENE MUTATIONS 51 



to 50 per cent of the cases. The reversion may occur in either 

 the germ cells, or in certain of the body cells. When the 

 reversion occurs in the germ cells, the offspring of the mutant 

 (small-winged) individuals are of the normal large- w^inged 

 type. When the reversion occurs in the body cells, those parts 

 of the wings derived from these reverted cells are of the nor- 

 mal large type, while the remaining parts of the wings are of 

 the miniature type. Thus mosaic individuals are produced, 

 portions of the wings large, other parts small, in the same 

 individual. In certain families reversion from mutated to 

 normal occurred frequently in the body cells, yielding mosaic 

 individuals; but never in the germ cells. 



Extreme cases of frequent, reversible, and inconstant muta- 

 tions are known in plants. Typical examples of these are seen 

 in variegated maize or Indian corn." In the variegated varie- 

 ties, parts of the same ear of corn show seeds of different 

 colors: red, yellow, white. Even single seeds on the ear may 

 be variegated; splashed or streaked with two or three colors 

 in small areas. The variegated condition is known to be due 

 to a single gene that differs from one of the genes in the 

 uniform varieties. 



When the variegated plants are bred together they give a 

 number of different sets of offspring, with different types of 

 coloration. Some of the offspring have the seeds mainly of one 

 color; some mainly of another color; some much variegated, 

 some all of one color. The diversities of color tend to be inher- 

 ited, showing that the differences in color are due to differ- 

 ences in the genes. If from a variegated ear there be selected 

 two seeds, one lighter in color, the other darker, the former 

 gives lighter offspring, the latter darker offspring — each still 

 with much variation. From a single seed of a certain single 

 color a plant may be produced having diverse colors in its 



