AN INTRODUCTION TO ZOOLOGY 



may be expressed diagrammatically as in Figure 157 (269). 

 Many other plants and numerous animals have been experimented 

 with; in some cases Mendel's law has been confirmed; in other 

 cases the inheritance is apparently determined in a different way. 

 To account for the inheritance of characters in the Mendelian 

 ratio of three dominants (D) to one recessive (R), the theory of 

 the segregation of germ cells has been proposed. This is that 

 the " germ cells or gametes produced by cross-bred organisms may 

 in respect of given characters be of the pure parental types, and 

 consequently incapable of transmitting the opposite character; 

 that when such pure similar gametes of opposite sexes are united 

 in fertilization, the individuals so formed and their posterity are 

 free from all taint of the cross; that there may be in short, per- 

 fect or almost perfect discontinuity between these germs in re- 

 spect of one of each pair of opposite characters " (Bateson). 



TALL 9.X DWARF-f OR DWARF 



* v O 



TALL (DWARF) 



PARENTS PRODUCE ALL 

 TALL DOMINANTS 

 CONTAINING DWARFNESS 

 IN A LATENT CONDITION 



HYBRID OFFSPRING WHEN 

 INBRED PRODUCE &/4 

 TALL AND 1 /4 DWARF 



DWARFS WHEN INBRED 

 BRED TRUE, ALWAYS 

 GIVING RISE TO DWARFS 



FIG. 157. Diagram showing the inheritance of tallness and dwarf ness in peas 

 according to Mendel's Law. (Modified after Thomson.) 



