Mutations A mutation is a spontaneous in the one or more bases of the DNA molecule, by insertion, deletion, or substitution.  Insertion and deletion will usually cause a very significant change in the DNA sequence. For example, the CCAUGTAUCGTG DNA sequence gives CCA, UGT, AUC, and GTG triplets. But the insertion of an A will give very different triplets. The new DNA sequence is CCAAUGTAUCGTG. Since the sequence of DNA is still going to be read in 3s, this will give you CCA, AUG, TAU, CGT. Thus an insertion of deletion will affect all the base sequence downstream of the DNA molecule. This will lead to the production of an entire set of totally different proteins. As a result, the mutants will have distinctive differences.  On the other hand, a substitution is relatively harmless. One base is changed to another, and only 1 amino acid may be changed. Mutants usually look similar to the normal ones, and their mutation may not be discovered without a thorough check up.  Mutations can sometimes produce useful qualities that will enhance the survival of the individual, but most of the times, its effect is disastrous. Victims suffer from mental retardation, organ disorder and ineffective body systems.   Relating Topics - Paternal and Maternal Chromosomes - Random Assortment        Here's an example of how the mutation of one nucleotide affects the shape and function of hemoglobin in blood. Defective cells are ineffective in oxygen transport. Heterozygotes exhibit the sickle cell trait. Homozygous individuals suffer from sickle cell anemia which can lead to death in childhood.