Question

A mutation is an heritable change in the dna of a cell. mutations are rare occurrences and are often caught by the cell's "proofreading" system during cell replication and so are not passed on to offspring. why is it more likely for an a nucleotide to mutate to a g nucleotide than to a t nucleotide?

Answer 1

DNA consists of two types of nitrogenous bases: Purine and Pyrimidine. Purine is a double ringed structure that includes Adenine (A) and Guanine (G) while pyrimidine is a single ringed structure that includes Thymine (T), Cytosine (C) and Uracil (U). In a DNA helix pairing takes place between one purine and one pyrimidine. A pairs with T and U (in case of RNA) and G pairs with C. During a mutation, it is more likely for A to get mutated to G than to T because A and G are similar in structure than T and C and the structure of DNA is not changed.