CHAPTER XXXIV 



MUTATIONS 



Hugo de Vries. 



Keystone View (Jo. 

 August Weismann. 



What are mutations? What is the ijnportance of viutationsf 



The theory of germ plasm. August Weismann (1834-1914), a 

 German biologist, tried to produce a race of tailless mice. He 

 cut off the tails of tiny baby mice as soon as they were born. When 

 these grew to adult mice, they mated and had offspring. These 

 baby mice had long tails. He repeated this experiment generation 

 after generation. Cutting the tails of the parent mice did not 

 affect the germ cells of either males or females. He then selected 

 mice with the shortest of stubby tails, mated them, and continued 

 to select the shortest-tailed mice for parents. xAfter several genera- 

 tions of this selecting and mating, a short-tailed race of mice was 

 produced. He had selected mice whose germ cells carried the gene 

 for short tails. 



As a result of this second experiment, Weismann formulated a 

 theory explaining why offspring resemble their parents. He 

 believed that the germ plasm does not arise anew in each organism, 

 but is actually received from its parents. Explained briefly, his 

 theory is this : Each new organism begins as a single cell, which is 

 pure germ plasm. In higher plants and animals this cell is formed 

 from the union of an egg and sperm. The cell, called a fertile egg, 

 begins to divide. Very early in this division, and before differ- 



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