Deletion

In genetics, a deletion is a type of mutation where one or more nucleotides (bases) are removed from a DNA sequence. Deletions can be as small as a single base removed or as large as an entire piece of chromosome lost, potentially eliminating multiple genes.

• A small deletion in a gene (if not in a multiple of 3 bases) will cause a frameshift mutation, likely rendering the gene's protein nonfunctional because the reading frame of the genetic code is disrupted.
• Larger deletions can remove important genes entirely. For example, a deletion on chromosome 5 causes Cri-du-chat syndrome, and a specific 3-base deletion in a gene (CFTR) is the most common cause of cystic fibrosis.
• Because genetic code is read in triplets, deletions of 3 (or multiples of 3) bases might only remove one or more amino acids but leave the rest of the protein's reading frame intact (possibly a milder effect compared to a frameshift).

• Look for clues like "a nucleotide is missing" or "a segment of DNA is lost" - that indicates a deletion mutation. Exam questions may ask the consequence, e.g., frameshift if in coding DNA.
• If presented with a DNA sequence comparison showing bases or chunks missing in the mutant, you're dealing with a deletion. A classic test example: original sequence vs mutant sequence with one base gone - students are asked about the effect on the protein (frameshift and likely premature stop codon).
• Sometimes exams highlight human disorders caused by deletions (to test understanding of mutations affecting phenotype). Knowing examples like the ones mentioned (e.g., cystic fibrosis 3-bp deletion, Cri-du-chat large deletion) can provide context.