OLD TYPES AND NEW 



147 



This distinction between atavism and reversion 

 becomes clearer by illustration. 



If heterozygous brown-eyed individuals mate, 

 there is one possibility in four that their offspring 



GRANDMOTHER GRANDFATHER 



HOMOZYGOTE 

 Duplex, 



I 

 \ 



HETEROZYGOTE HOMOZYGOTE HETEROZYGOTE 

 Simplex Duplex v _ fj .. Simplex 



FIQ. 48. Three generations of a Mendelian monohybrid. The outlines 

 represent the somatoplasms with the phenotypic character on the out- 

 side. The black symbols inclosed within the somatoplasm stand for 

 the germplasm in the form of gametes. The short dotted arrows indi- 

 cate the relation between germplasm and somatoplasm. The long 

 dotted arrows indicate possible recombinations of germplasms. 



will have blue eyes unlike their own, but like the two 

 blue-eyed grandparents. Such a blue-eyed child 

 would be an instance of atavism. The explanation 



