Mutation (Class - XII)

5-Bromouracil induces transitions, not transversions.

This is a transition mutation because A is mutated to G.

Frameshift mutation affects more than one amino acid. Due to the triplet nature of gene expression by codons, the insertion or deletion can change the reading frame resulting in a completely different translation from the original.

Due to tautomeric shift, the more stable keto form of guanine changes to less stable enol form and pairs with thymine.

Loss of a purine base (A or G) to form an apurinic site (AP site) is depurination, which results into spontaneous mutation. AP site has neither a purine nor a pyrimidine base, either spontaneously or due to DNA damage.

DNA polymerase I is involved in checking errors during DNA replication and performing excision repair.

Acridine dyes induce frameshift mutations.

In tautomeric shift, hydrogen atoms move from one position in a purine or pyrimidine to another position; for example, from an amino group to a ring nitrogen.

UAU codes for tyrosine and UAG codes for stop codon; so non-sense mutation has taken place.

In both cases, i.e. falciparum resistance and abnormal mucus production, mutation in one gene results in more than one phenotypic trait. Thus, both are examples of pleiotropy.

Mutation known as CCR5-Δ32 in the CCR5 gene imparts protection against HIV.

A change in a single nucleotide in DNA changes the corresponding nucleotide in mRNA, resulting in a different codon that codes for a different amino acid.

A neutral mutation has no harmful or beneficial effect on the organism. Such mutations occur at a steady rate, forming the basis for the molecular clock. In the neutral theory of molecular evolution, neutral mutations provide genetic drift as the basis for most variation at the molecular level.

UV radiations induce mutation by formation of thymine dimer. Dimers ultimately perturb the DNA double helix and interfere with accurate DNA replication.

Muller used drosophila in his experiments to induce mutation by X-rays in 1927. He was the first to demonstrate that mutations could be induced by an external factor.