The effect of base-pair substitution mutations on protein function varies widely from no detectable effect to the complete loss of protein function (null allele). Why do the functional consequences of base-pair substitution vary so widely?

Two different mutations are identified in a haploid strain of yeast. The first prevents the synthesis of adenine by a nonsense mutation of the ade-1 gene. In this mutation, a base-pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA). The second affects one of several duplicate tRNA genes. This base-pair substitution mutation changes the anticodon sequence of a tRNAᵀʳᵖ from

   3′−ACC−5′ to 3′−ACU−5′

Do you consider the first mutation to be a forward mutation or a reversion? Why?

Researchers interested in studying mutation and mutation repair often induce mutations with various agents. What kinds of gene mutations are induced by

Chemical mutagens? Give two examples.

In numerous population studies of spontaneous mutation, two observations are made consistently: (1) Most mutations are recessive, and (2) forward mutation is more frequent than reversion. What do you think are the likely explanations for these two observations?

Researchers interested in studying mutation and mutation repair often induce mutations with various agents. What kinds of gene mutations are induced by

Radiation energy? Give two examples.

Describe the purpose of the Ames test. How are his⁻ bacteria used in the Ames test? What mutational event is identified using his⁻ bacteria?

Ultraviolet (UV) radiation is mutagenic.

Identify and describe two DNA repair mechanisms that remove UV-induced DNA lesions.