When the amino acid sequences of insulin isolated from different organisms were determined, differences were noted. For example, alanine was substituted for threonine, serine for glycine, and valine for isoleucine at corresponding positions in the protein. List the single-base changes that could occur in codons of the genetic code to produce these amino acid changes.

Most mutations are thought to be deleterious. Why, then, is it reasonable to state that mutations are essential to the evolutionary process?

Why is a random mutation more likely to be deleterious than beneficial?

Most mutations in a diploid organism are recessive. Why?

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?

What is the difference between a silent mutation and a neutral mutation?

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

In studies of the amino acid sequence of wild-type and mutant forms of tryptophan synthetase in E. coli, the following changes have been observed:

Determine a set of triplet codes in which only a single-nucleotide change produces each amino acid change.

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?