Tag: mutational theory of evolution

Neo-Darwinism, Theory of evolution that represents a synthesis of Charles Darwin's theory in terms of natural selection and modern population genetics. The term was first used after 1896 to describe the theories of August Weismann (18341914), who asserted that his germ-plasm theory made impossible the inheritance of acquired characteristics and supported natural selection as the only major process that would account for biological evolution. A few supporters of neo darwinism are Romanes, Wallace, Fisher, Huxley, Ford, Haldane, Sewall Wright, Ernst Haeckel, August Weismann, Herbert Spencer and Hugo de Vries etc. 

• In biology, a mutation is the alteration of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA.
•  Mutations result from errors during DNA replication or other types of damage to DNA such as may be caused by exposure to radiation or carcinogens.
• Hence, gene frequency in a population remains stable, unless and until there is a mutation. 
• So, the correct answer is 'Mutation'.

Mutations are sudden changes in the characteristics of organisms due to chemical changes in the genetic material. The theory of mutation was proposed by Hugo De Vries. Charles Darwin gave the theory of natural selection and Neo-Darwinism is an advanced version of darwins theory.

The term mutation was introduced by Hugo de Vries, while working on evening primrose. He observed aberrent types in $F _1$ generation of two pure breeding varieties. The sudden appearance of new characters was termed as mutation, which he defined as sudden, discontinuous, inheritable changes in genetic material. 

The concept of sudden genetic change, which breeds true in an organism is visualized as a mutation. Any sudden or spontaneous change in character which is inheritable is known as mutation. It is defined as the changing of the structure of a gene, resulting in a variant form which may be transmitted to subsequent generations, caused by the alteration of single base units in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes.

Hugo de Vries studied inheritance of flower colour in Oenothera lamarckiana (evening primrose) and proposed mutation theory that says that mutations are sudden, random, and inheritable and discontinuous variations which serve as raw material for evolution. 

a) Theory of evolution was given by De Vries in 1901 which states that evolution is a process where new species are formed due to mutations that functions as a raw material for evolution.

Example for harmful effect of mutation: Oncogenes are harmful mutations can cause cells to become malignant and can ultimately lead to cancer. Mutations are mostly harmful and sometimes neutral (silent mutations)

According to Dobzhansky, mutations, which help organisms in its survival, in the changing environment are accumulated in its genetic composition by natural selection. Mutations are now considered as the ultimate source of organic evolution. By mutations, some old genes can be replaced by new genes in a population to develop changes and thus, mutations play important part in the process of organic evolution.
Thus, the correct answer is option (D), 'Mutation'.

Hugo de Vries gave mutation theory and felt the importance of chance events i.e., mutations during evolution. This was against Darwinian view of evolution as a slow directional process. Mutations are random chance events and result in sudden evolution of characters in a single or few generations.