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THE NEW INDIVIDUAL 



Part IV 



Pentaploid 

 5X 



Tefraploid 

 4X 



Haploid 

 IX 



Fig. 20.23. Giant cells. Polyploidy in salamanders (Tri turns viridescens) . The 

 salamander larvae are all at about the same stage of development. Since they are 

 about the same size, the changes in cell size due to polyploidy result in a reduced 

 number of body cells. (Courtesy, G. Fankhauser, Princeton University.) 



cessives, often defects, are hidden by dominants. Cross breeding of plants 

 or animals of different varieties leads to increased vigor. This is often de- 

 scribed as hybrid vigor, for example, the offspring of a male ass and a mare 

 is a mule, a hybrid tougher than either parent. 



Mistaken Ideas about Heredity 



Acquired Characters. Nothing is inherited unless it changes the genes in 

 the sex cells. Bodily injuries do not do this; neither do acquired habits or 

 training — eating olives or building bridges. An overwhelming number of 

 experiments and arguments has been presented in fruitless attempts to prove 

 that effects upon muscles, nerves, and bones may be inherited. Tails of rats 

 bobbed for many generations have left the last generation of rats growing 

 tails as long as those of the first; the sex cells are untouched by the afflictions 

 of the tails. Only the capacity is inherited, a tail to be cut, a mind to be trained. 



Does one or the other parent take a greater part in inheritance? Only if 

 one has the dominant members of pairs of genes and the other the recessives. 

 A recessive must await its chance of expression until it can pair with another 

 recessive. 



Telegony. This is a theory that in case two or more males mate with one 



