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level: 20.1 Gene mutations

Questions and Answers List

level questions: 20.1 Gene mutations

QuestionAnswer
Substitution of bases- A nucleotide is replaced by another nucleotide that has a different base - Can form stop codon - So production of the polypeptide would be stopped prematurely - Final protein different, not perform its normal function - Forms codon for a different amino acid, structure of polypeptide different, different shape + not function properly - Forms different codon but for the same amino acid, genetic code is degenerate, has no effect
Deletion of bases- Causes frame shift - Most triplets will be different, amino acids different too - Polypetides different, nonfunctional protein, could alter phenotype - One deleted base at the very start of a sequence could alter every triplet in the sequence - A deleted base near the end of the sequence is likely to have a smaller impact but can still have consequences
Other types of gene mutation- Addition of bases - Duplication of bases - Inversion of bases - Translocation of bases
Addition of bases- An extra base becomes inserted in the sequence - Usually causes frame shift (right) + the whole sequence of triplets becomes altered
Duplication of bases- One or more bases are repeated. This produces a frame shift to the right. CGG AAA AAA CGC
Inversion of bases- A group of bases become separated from the DNA sequence and rejoin at the same position but in the inverse order (back to front) - The base sequence of this portion is therefore reversed and effects the amino acid sequence that results
Translocation of bases- A group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome - Often have significant effects on gene expression leading to an abnormal phenotype e.g. dev. of certain forms of cancer and also reduced fertility