Each amino acid in a protein is coded as three codons or bases.
If any one of the codons is incorrect, the amino acid will be also incorrect. There is a "wobble" effect in the last base so there can be some neutral effect.
But if the base is incorrect at the first or second spot in the codon, there is a good chance that the protein will be incorrect (a mutation). Most of our enzymes are proteins as well as many hormones and tissues. These will not work correctly and the result will be a malfunction where these proteins are needed.
Think of all the steps in the metabolic processes that will come to an abrupt halt.
DNA sequencing is the process of determining the precise order of nucleotides within a DNA molecule.
It includes any method or technology that is used to determine the order of the four bases adenine, guanine, cytosine, and thymine in a strand of DNA.
The canonical structure of DNA has four bases: Thymine (T), Adenine (A), Cytosine (C), and Guanine (G). DNA sequencing is the determination of the physical order of these bases in a molecule of DNA.
The most popular method for doing this is called the dideoxy method or Sanger method named after Frederick Sanger, who was awarded the 1980 Nobel prize in chemistry.
Knowledge of DNA sequences has become indispensable for basic biological research, and also in applied fields such as: diagnostic, biotechnology, forensic biology, virology, ...https://www.youtube.com/watch?v=91294ZAG2hg