05 Origin and Evolution of life - part 06 - Mutation Theory

05 Origin and Evolution of life - part 06 - Mutation Theory


Mutation Theory : 
  • This theory was proposed by Hugo de Vries(1901), after the rediscovery of Mendel's work (1900). 
  • He proposed this theory based on his observations on seven generations of the plant evening primrose (Oenothera Lamarckiana). 
  • He found that though most of the offsprings resembled their parents in many characters, some of the offsprings show the appearance of sudden or spontaneous variation clearly different from the phenotypic expression of the parent. 
  • These sudden variations were called mutations or discontinuous variations. 
  • The variant offsprings produced variants and not normal plants i.e. these changes were inheritable. 
  • He also observed that some variants also produced more variations. 
  • He noted that these sudden changes are inheritable, and proposed the Mutation theory. 
  • The main features of mutation theory are :
  1. Mutations are large, sudden and discontinuousvariations in a population. These changes are inheritable. 
  2. Mutations provide the raw material for organic evolution. 
  3. Mutation may be useful or harmful. 
  4. Useful mutations are selected by nature.
  5. Accumulation of these mutations over a period of time leads to the origin and establishment of new species. 
  6. Harmful mutation may persist or get eliminated by nature.
Objections to Mutation Theory : 
  • The large and discontinuous variation observed by Hugo de Vries were actually due to chromosomal aberrations were as gene mutations usually bring about minor changes. 
  • Rate of mutation is very slow as compared to the requirement of evolution. 
  • Chromosomal aberrations have little significance in evolution as they are quite unstable.
Always Remember :
  • According to Darwin variations are small and directional where as mutations are large, sudden, random and direction less.  
  • Darwin believed that the gradual inheritable variations over a long period of time, lead to Speciation (formation of new species) while de Vries believed that mutations are the cause of speciation. 
  • A single step large mutation is called saltation. 

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