If a base-pair change occurs in DNA, this a. is a mutation. b. would be a mutation only if it falls in a protein-coding part of a gene. c. would be a mutation only if it falls in a transcribed part of the genome. d. is not a mutation, because only one base pair has been altered.

Which of the following is an important exception to the central dogma of molecular biology?

a. Many genes code for RNAs that function directly in the cell.

b. DNA is the repository of genetic information in all cells.

c. Messenger RNA is a short-lived 'information carrier.

d. Proteins are responsible for most aspects of the phenotype.

DNA's primary structure is made up of just four different bases, and its secondary structure is regular and highly stable. How can a molecule with these characteristics hold the information required to build and maintain a cell?

Which of the following describes the experimental strategy that was used to decipher the genetic code?

a. Comparing the amino acid sequences of proteins with the base sequence of their genes

b. Analyzing the sequence of RNAs produced from known DNA sequences

c. Analyzing mutants that changed the code

d. Examining the polypeptides produced when RNAs with particular sequences were translated

A friend says, 'Geneticists spend all their time talking about DNA, but that's silly because DNA really isn't that important in the functions of a cell.' In what ways is she right, and in what ways might she be wrong?

A minimal genetic code requires only 21 codons—one for each amino acid, and one for a stop signal. Given this, what advantage might be offered by having a code with 64 codons?

Which of the following describes mutations? Select True or False for each statement.

T/F Point mutations can occur in any DNA sequence.

T/F Frameshift mutations can occur in any DNA sequence.

T/F Neutral mutations depend on the degeneracy of the genetic code.

T/F Deleterious mutations occur only in protein-coding sequences of DNA.

Explain what's wrong with this statement: All point mutations change the genotype and the phenotype.

Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.)

(a) Suppose a mutation made the gene for enzyme C nonfunctional. What molecule would accumulate in the affected cells?

Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.)

(b) Suppose a mutant strain can survive if substrate 5 is added to the growth medium, but it cannot grow if substrates 1, 2, 3, or 4 are added. Which enzyme in the pathway is affected in this mutant?

One of the possibilities considered about the genetic code was that the code was overlapping, meaning that a single base could be part of up to three codons. How many amino acids would be encoded in the sequence 5′-AUGUUACGGAAU-3′ by a non-overlapping and a maximally overlapping triplet code?

a. 4 (non-overlapping) and 16 (overlapping)

b. 4 and 12

c. 4 and 10

d. 12 and 4

Skin color is often one of the first traits people notice in each other. Studies in zebrafish uncovered a mutation that altered a transport protein and resulted in light-colored fish. This discovery led to the finding that the same gene in humans has a strong influence on skin pigmentation in many populations. The zebrafish mutation that reduced coloration created a null allele of the transport protein gene. Which of the following types of mutation would be most likely to create this null allele?

a. A missense mutation

b. A frameshift mutation

c. A neutral mutation

d. A silent mutation

Investigators examined the expression of transporter mRNA and protein produced in zebrafish homozygous for each of the alleles and obtained the results summarized here (+ = present, −= absent). Does the allele associated with light color appear to be altering transcription or translation? Why?

A small portion of the human transport protein amino acid sequence is shown here. The upper sequence is associated with darker skin, and the lower sequence is associated with lighter skin. What DNA base-pair change created the light-skin form of the human protein from the gene that coded for the dark-skin form?

Researchers compared the amino acid sequences of the transport protein in zebrafish, puffer fish, mice, and humans. They found many stretches with identical sequences in all four species. Does this mean that the corresponding mRNA base sequences are also the same in these four species? Explain why or why not.

The allele of the human transport protein associated with lighter skin is found almost exclusively in people with European ancestry. The other common allele for darker skin, which appears to be the ancestral allele, is found in people with African ancestry. What is a plausible explanation for how the lighter-skin allele came to be so common in those with European ancestry?