Theory of Mutation

Mutation Theory

Hugo de Vries (1901) first used the term Mutation means sudden change.

“Theory states that evolution takes place by sudden changes small and large in individual, these are inheritable” Darwin named it sports ; Bateson (1894) termed it as discontinuous or saltatory variation Hugo de Vries observed this in wild plant, Oenothera lamarckiana (Evening Primrose) and concluded:

New species arise by sudden jump (saltation) or a single step large mutation (macrogenesies)

• Mutations attain full constancy and are inherited to next generation
• The resultant one i.e., “mutant” is a pure breed. The progeny of mutant marks the beginning of new species, when produced in large number.
• All organisms have the traits or tendency to mutate but it occurs under the influence of environment.
• Being indeterminate it can occur either way, i.e., complete loss of some parts or gain of a new part, it may be useful or harmful (lethal).
• Mutation’s are recurring in nature and so the same mutation may appear again and again, this increases the chance of selection.
• Different kind of mutation can occur in different members of the same species.

Natural selection to Mutation

Darwin de Vries:

Emphasised the adaptive nature of variation Stressed on randomness of variation Highlighted the importance of small and Focused on abrupt and often drastic changes as cause of gradual differences in evolution origin of species Darwinism revealed that evolution resulted New species could arise by sudden jump often called from gradual fluctuating inheritable, saltation or through a single step large mutation variations over a long series of (Macrogenesis) generations Natural selection as main evolutionary Mutation as main evolutionary force

Criticism of de Vries mutation theory

David, Jeffrey and others pointed out that Oenothera is highly inconsistent hybrid species. Conclusions are not well founded, which was mainly due to unstable chromosomal aberration (change in number) Being random in nature mutations are hardly useful for adaptability which is important for evolution. Mutations are incapable of introducing new genes or alleles into a gene pool, and natural selection becomes operative only after this. Darwin & Lamarck stressed upon adaptive nature of variation whereas de Vries believed in its randomness.

Modern Views of Darwinism

Although de Vries’ idea raised suspicion against natural selection among geneticists yet it helped in better understanding of Darwinism.

Besides the macroevolution there is also microevolution (change at genetic level) The study of evolution based upon population genetics led to the emergence of comprehensive ideas presented as “ Modern synthetic theory ”.

Population Genetics and Evolution

Population is the number of all individual of same species in a defined area at a particular time. As per modern synthetic theory population is the unit of evolution.

Population genetics is related to the study of frequency of genes in a population .It is the application of Mendelian genetics to Darwin’s theory of natural selection Evolution occurs within a population when relative frequency of DNA changes.

Hardy - Weinberg Law

Proposed by G.H. Hardy and W. Weinberg in 1908 independently. The law states “the frequency of genes or alleles in a population remains constant through generations if all other factors are constant”, this is called genetic equilibrium, evolution occurs when this equilibrium is deviated. Hereditary conservation of genes is the characteristic of a population. The extent of evolution depends upon the degree of deviation. Thus it provides a tool to the geneticist to determine when evolution is going to occur. Five basic processes affect the Hardy - Weinberg equilibrium to cause variation at genetic level, these are mutation, recombination, gene migration, genetic drift and natural selection.