15. Gene Expression

Which of the following mutations, occurring just after the start codon in the mRNA is likely to have the most serious effects on the polypeptide product?

A nonsense mutation:

A single base substitution is LEAST likely to be deleterious (dangerous) when the change results in _____.

 A section of DNA has this base sequence: AGCGTTACCGT. A mutation in this DNA strand results in this base 

sequence: AGGCGTTACCGT. What type of mutation does this change represent?

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.

If a fragment of a chromosome breaks off and then reattaches to the original chromosome but in the reverse direction, the resulting chromosomal abnormality is called a. a deletion. b. an inversion. c. a translocation. d. a nondisjunction.

Imagine discovering a loss-of-function mutation in a eukaryotic gene. You determine the gene's nucleotide sequence from the start site for transcription to the termination point of transcription and find no differences from the wild-type sequence. Explain where you think the mutation might be and how the mutation might be acting.

Which of the following mutations would be most likely to have a harmful effect on an organism? a. a deletion of three nucleotides near the middle of a gene b. a single nucleotide deletion in the middle of an intron c. a single nucleotide deletion near the end of the coding sequence d. a single nucleotide insertion downstream of, and close to, the start of the coding sequence

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.

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?

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?