Gene Mutations.

A gene is a long sequence of nucleotides on a DNA molecule. A mutation is a change in the amount of an organism's genetic material and when a change in genotype produces a change in phenotype, the individual affected is said to be a mutant. A gene mutation involves a change in one or more of the nucleotides in a strand of DNA. The sequence of nucleotides in a gene controls the order in which …

…mutations only bring about a minor change and sometimes the organism is only affected slightly or not at all, however if a substituted amino acid occurs in a critical position in the protein then a major defect may arise. Frameshift mutations lead to a major change since it causes a large portion of the gene's DNA to be misread. The protein produced differs from the normal protein by many amino acids and is usually non-disfunctional.