Answer:
DNA is divided into codons which are 3 bases long. Each codon codes for a specific amino acid or signals transcription to stop or start. Inserting or deleting one base pair changes how the DNA is read, so it will often alter the amino acids the DNA sequence produces. As a result, the protein made from the gene may not function properly.
Example:
AAT CGC CGA TGA
Delete the T from the first codon
AAC GCC GAT GA
The entire sequence is read differently ^
