Mutations
Charles Darwin (1859) in his book ' Origin of Species ' postulated that evolution or formation of newer species of organisms from the pre-existing ones occurs through accumulation of variations in the organisms. Without variations all the individuals of a species shall be alike. None of them would have better characteristics for being favoured in the struggle for existence and natural selection. A change in the environment could kill all of them. Variations increase the adaptability of the individuals and make them better fitted in the struggle for existence and hence natural selection. There are two sources of variations in the populations - recombinations and mutations . (i) Recombinations are also called continuous variations . They are not new traits but are formed by new combination of genes or traits already existing in the population. Recombinations are produced due to three reasons: (a) Crossing over of nonsister chromatid segments during meiosis. (b) Random segrega