Question

Which type of mutation causes the most damage?

Answer 1

A mutation occurs when the sequence of DNA changes. Mutations can occur as a consequence of DNA copying errors during cell division, exposure to ionising radiation, exposure to substances known as mutagens, or viral infection. Somatic mutations occur in body cells and are not passed on to children, but germ line mutations occur in eggs and sperm and can be passed onto offspring.

Complete solution:
A Mutation is defined as change in the structure or sequence of DNA due to physical, biological or chemical means, which ultimately lead to an altered product (mutant product)being translated from the changed DNA (mutated DNA).
Mutations caused by insertion or deletion of nitrogenous bases in the DNA sequence leads to the most damage to DNA since it completely changes the reading frame for the process of protein synthesis.
Insertion or deletion that results in frameshift mutation are considered as the most damaging mutation. It induces alterations in the amino acid sequences of following amino acids in a polypeptide chain. A point mutation only affects one amino acid, but a frameshift mutation affects the whole amino acid sequence after the change.
A frameshift mutation (also known as a framing mistake or reading frame shift) is a genetic mutation produced by the insertion or deletion of several nucleotides in a DNA sequence that is not divisible by three. The insertion or deletion of a codon might modify the reading frame, resulting in a completely different translation from the original due to the triplet structure of gene expression via codons.

Note:
Mutagens are substances that damage DNA and can cause permanent changes (mutations) in the DNA sequence, depending on an organism's capacity to repair the damage. Mutagens are chemical substances or types of radiation (such as UV light or X-rays) that produce irreversible and heritable changes (mutations) in the cellular genetic material, deoxyribonucleic acid (DNA).