Ch 14 Getting Ready for Exam

According to Figure 14.2, the average number of new mutations that occur across an entire human genome in one generation is approximately _____ times higher than in nematodes.

100

In the sickle-cell anemia mutation, the 5′-GAG-3′ codon for glutamic acid becomes the 5′-GUG-3′ codon for valine. Assuming a single nucleotide substitution accounts for this mutation, what is the change in the DNA?

3′-CTC-5′/5′-GAG-3′' to 3′-CAC-5′/5′-GTG-3′

In the standard genetic code (Table 4.1, shown below), how many codons for amino acids allow synonymous mutations in the third position?

59

The process of gene duplication and divergence refers to: (Select all that apply.) a) the creation of gene families, which are similar genes within a species. b) creating new genes by mutation in duplicates of old genes. c) the creation of new species as new genes are created from duplicates of old genes. d) offspring becoming increasingly different from their ancestors. e) None of the answer options is correct.

a and c

Why do data on observable mutant phenotypes underestimate the actual frequency of mutation? (Select all that apply.) a) Many mutations are in noncoding regions of the genome. b) Most mutations result in death of the individual or an inability to reproduce. c) Some mutations in protein-coding regions of the genome are synonymous mutations.

a and c

A family can share a genetic risk of developing cancer if: a) the cancer is caused by germ-line mutations. b) a somatic cell mutation in one of the genes implicated in the cancer occurred in an ancestor. c) the cancer is caused by somatic cell mutations. d) a germ-line mutation in one of the genes implicated in the cancer occurred in an ancestor. e) All of these choices are correct.

a germ-line mutation in one of the genes implicated in the cancer occurred in an ancestor

Any heritable change in the genetic material is _____.

a mutation

Cancer is usually due to:

a series of mutations that occur in a single lineage of somatic cells.

Some people with blue eyes have a small sector of one eye that is brown. What kind of mutation could cause this color difference?

a somatic mutation late in development

Point mutations can impair a protein if they result in a: (Select all that apply.) a) nonsense codon. b) shift in reading frame. c) synonymous codon. d) nonsynonymous codon.

a, b, and d

Which of the following statements concerning cancer and mutations is CORRECT? a) Cancer can only occur with a mutation in a somatic cell. b) Usually, multiple mutations are required in different genes to cause cancer. c) Cancer can only occur with a mutation in a germ cell. d) Usually, a single mutation is all that is required to cause cancer. e) None of the other answer options is correct.

b

The most frequent kind of mutation, a point mutation, occurs when: (Select all that apply.) a) DNA repair mechanisms fail. b) a block of nucleotides is rearranged. c) a single base pair is replaced by another. d) open reading frames are altered. e) None of the other answer options is correct.

c

Insertions and deletions of single nucleotides:

cause frameshift mutations

A nonsense mutation:

changes a codon for an amino acid into a codon for chain termination

Which of the following point mutations is unlikely to change a protein's ability to function? (Select all that apply.) a) one that creates a new codon that codes for an amino acid of the same size as that coded for by the original codon b) one that occurs in somatic cells c) one that occurs in germ cells d) one that occurs in a noncoding region of DNA e) one that creates a new codon code for the same amino acid as the original codon

d and e

Why do RNA viruses and retroviruses have such high rates of mutation? (Select all that apply.) a) because viral RNA can form stem-and-loop structures b) because RNA viruses and retroviruses initially cause host-cell mutations during replication c) because RNA polymerase is an unstable enzyme d) because viral polymerases lack a proofreading mechanism e) because RNA is more fragile than DNA and is therefore more likely to be damaged

d and e

The American Cancer Society currently estimates that only about 10% of all people with melanoma have a family history of the disease. What factors might contribute to the development of melanoma in the other 90% of patients? a) exposure to solar radiation b) exposure to chemical mutagens c) mutations in a melanocyte d) All of these choices are correct.

d) All of these choices are correct.

Large chromosomal inversions can cause problems in which of the following processes? a) mitosis b) reciprocal translocation c) mismatch repair d) meiosis e) None of the answer options is correct.

d) meiosis

Deletions that eliminate a multiple of three nucleotides can:

delete amino acids in a polypeptide chain.

Which of the following types of mutation is typically harmful?

deletion of the centromere

The drawings below represent several different versions of human chromosome 2. In each one, the gray region of the chromosome represents the gene that codes for the light chain of the myosin protein (the drawing is not to scale). Diagram 1 represents the nonmutant human chromosome 2. Among diagrams 2 through 4, which represents a mutation of chromosome 2?

diagrams 2, 3, and 4

You are working in a lab and studying a gene. You notice that many other genes in the same organism code for similar proteins. This is MOST likely the result of:

duplication and divergence

_____ is the process where new genes evolve from duplicates of old ones.

duplication and divergence

In a muscle cell, myosin binds to actin to cause muscle contraction. Researchers have found that rabbit muscle myosin binds to actin from an amoeba. How can this be? a) The myosin from amoeba and rabbits is similar due to a distant common ancestor, and the differences between them do not affect the actin binding site. b) The myosin from amoeba and rabbits is similar due to a distant common ancestor. c) Proteins whose functions are important to many types of organisms are more likely to be conserved. d) The differences in myosin between amoeba and rabbits do not affect the actin-binding site of myosin. e) All of these choices are correct.

e) All of these choices are correct.

Chromosomes in which the normal order of a block of genes is reversed contain a(n):

inversion

Imagine a gene in which the sequence that is transcribed into a GAG codon, which codes for glutamic acid, is mutated to GUG, which codes for valine. What type of mutation is this?

missense

Sickle-cell anemia results from what type of mutation?

missense

The relatively large number of new mutations that occur in the human genome in each generation is tolerable because:

most of our genome is noncoding DNA, so few mutations affect our proteins.

An agent that increases mutation rate is a _____

mutagen

Consider the single methionine codon 5′-AUG-3′ in the standard genetic code. Can a single base change in this codon create a synonymous mutation? Can a single base change in this codon create a stop codon?

no, no

Consider the tryptophan codon 5′-UGG-3′ in the standard genetic code (Table 4.1, shown below). Can a single base change in this codon create a synonymous mutation? Can a single base change in this codon create a nonsense codon?

no, yes

A point mutation that creates a premature stop codon is called a _____ mutation.

nonsense

A point mutation that causes an amino acid replacement is called a:

nonsynonymous (missense) mutation

Point mutations that cause amino acid replacements are called:

nonsynonymous (missense) mutation

Each curve in the graph below shows the proportion of amino acid between a protein in two species that diverged from a common ancestral species. Which protein is the MOST conserved (i.e., changes most slowly in sequence)?

point L (horizontal line)

Chronic myelogenous leukemia (CML) is caused when a segment of chromosome 9 and a segment of chromosome 22 both break off and switch places. How is this mutation classified?

reciprocal translocation

When nonhomologous chromosomes exchange parts, a(n) _____ has occurred

reciprocal translocation

A point mutation that causes no change in the amino acid sequence of a protein is called a

synonymous (silent) mutation.

Normally, in corn, genes for waxy and virescent kernel appearance are in the same chromosome. In a certain stock, however, it was found that these two genes are in different chromosomes. Which chromosomal aberration would explain this?

translocation

Movable DNA sequences are called:

transposable elements.

A chemical agent that interferes with DNA repair may be considered a mutagen. true or false?

true

A chromosomal mutation in which a segment is missing is called a deletion. True or false?

true

Only germ-line mutations are transmitted to the progeny. True or false?

true

What causes breaks in one or both of the sugar-phosphate backbones?

x-rays

The enzyme _____ repairs breaks in the DNA sugar-phosphate backbone.

DNA ligase

The enzyme _____ repairs 99% of mismatched bases immediately during replication

DNA polymerase

Which of the following statements MOST accurately describes the benefits of the proofreading function of DNA polymerase?

DNA polymerase can repair most mutations as they occur during DNA replication

_____ mutations are important to the evolutionary process; most cancers result from _____ mutations.

Germ-line; somatic

The human genome contains a family of genes that code for different forms of myosin. How could this gene family have arisen?

The original myosin gene was duplicated, and the resulting copies have diverged.

Two independent mutants are discovered in a strain of fruit flies. Both are due to the insertion of a transposable element into a gene that is required to produce red pigment in the eyes, but the eyes are yellow instead of red. When the transposon undergoes transposition to another location, the copy present in the original location is sometimes deleted. When the copy in the gene required for red pigment is deleted, the gene regains its ability to function, and the cell with the deletion and all its descendants can produce the red pigment. In one mutant, A shown below, the eyes have tiny red sectors scattered throughout, whereas in the other mutant, B, the eyes have larger blotches of color. What do these patterns tell you about the transposition of the transposons in the mutants A and B?

The transposon in A tends to transpose at a later time in development than that in B

Which of the following statements applies to frameshift mutations?

They change the amino acid sequence downstream from the mutant site.