Sudden and a heritable change in a character/gene of an organism is 

Sudden and a heritable change in a character/ gene of an organism is mutation. Mutation is sudden, discontinuous variation in genotype and phenotype of an organism due to change in chromosomes and genes. In addition to recombination, mutation is another phenomenon that leads to variation in DNA. A point mutation is a change of a single base pair in DNA. Some mutations involve changes in whole set of chromosomes (polyploidy) or change in a subset of chromosome number (aneuploidy). So, the material for organic evolution is mutation because mutation leads to evolution.