15. Gene Expression

A point mutation in which a single base pair is inserted or deleted from DNA is called a(n) __________.

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A virus infects a cell and randomly inserts many short segments of DNA containing a stop codon throughout an organism's chromosomes. This will probably cause __________.

Which type of mutation is least likely to affect protein function?

1008

A particular mutation had no effect on the polypeptide encoded by a gene. This mutation probably involves __________.

802

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.

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?

517

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.

600

A geneticist found that a particular mutation had no effect on the polypeptide encoded by a gene. This mutation probably involved a. deletion of one nucleotide. b. alteration of the start codon. c. insertion of one nucleotide. d. substitution of one nucleotide.

1070

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.

903

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.

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

504

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

599

A mutation in a single gene may cause a major change in the body of a fruit fly, such as an extra pair of legs or wings. Yet it probably takes the combined action of hundreds or thousands of genes to produce a wing or leg. How can a change in just one gene cause such a big change in the body?

786

A chemical called dioxin is produced as a by-product of some chemical manufacturing processes. This substance was present in Agent Orange, a defoliant sprayed on vegetation during the Vietnam War. There has been a continuing controversy over its effects on soldiers exposed to it during the war. Animal tests have suggested that dioxin can be lethal and can cause birth defects, cancer, organ damage, and immune system suppression. But its effects on humans are unclear, and even animal tests are inconclusive. Researchers have discovered that dioxin enters a cell and binds to a protein that in turn attaches to the cell's DNA. How might this mechanism help explain the variety of dioxin's effects? How might you determine whether a particular individual became ill as a result of exposure to dioxin?

408

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?

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