AP BIOLOGY

Detailed explanation-1: -A nonsense mutation occurs in DNA when a sequence change gives rise to a stop codon rather than a codon specifying an amino acid. The presence of the new stop codon results in the production of a shortened protein that is likely non-functional.

Detailed explanation-2: -A nonsense mutation also differs from a nonstop mutation, which is a point mutation that removes a stop codon. About 10% of patients facing genetic diseases have involvement with nonsense mutations.

Detailed explanation-3: -Similar C-terminally extended proteins are constitutively produced when a stop codon is mutated to code for an amino acid; in both cases, this can lead to potentially deleterious proteins.

Detailed explanation-4: -Premature stop mutations can arise as a result of mutations within germline or somatic DNA, inaccurate or inefficient pre-mRNA splicing, or improper RNA editing. According to the Human Gene Mutation Database, 12% of all mutations reported are singlepoint mutations that result in a premature stop codon.

Detailed explanation-5: -Point mutations in a DNA sequence that cause the replacement of the normal codon for an amino acid by one of the three termination (or “stop”) codons are callednonsense mutations.