Chapter 14, Gene Mutation, DNA Repair, and Transposition Video Solutions, Essentials of Genetics

Problem 1

In this chapter, we focused on how gene mutations arise and how cells repair DNA damage. At the same time, we found opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter,
(a) How do we know that many cancer-causing agents (carcinogens) are also mutagenic?
(b) How do we know that certain chemicals and wavelengths of radiation induce mutations in DNA?
(c) How do we know that DNA repair mechanisms detect
and correct the majority of spontaneous and induced mutations?

Marisa A

Numerade Educator

00:45

Problem 2

Review the Chapter Concepts list on p. $261 .$ These concepts relate to how gene mutations occur, their phenotypic effects, and how mutations can be repaired. Write a short essay contrasting how these concepts may differ between bacteria and eukaryotes.

Jennifer Stoner

Numerade Educator

01:27

Problem 3

What is a spontaneous mutation, and why are spontaneous mutations rare?

Patina Herring

Numerade Educator

00:46

Problem 4

Why would a mutation in a somatic cell of a multicellular organism not necessarily result in a detectable phenotype?

Mikayla Stephens

Numerade Educator

02:28

Problem 5

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

Mathew Botros

Montclair State University

02:28

Problem 6

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

Mathew Botros

Montclair State University

02:24

Problem 7

Most mutations in a diploid organism are recessive. Why?

Vivek Singh

Numerade Educator

01:53

Problem 8

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

Carlene Jimenez

Numerade Educator

00:19

Problem 9

Describe a tautomeric shift and how it may lead to a mutation.

Sam Limsuwannarot

Numerade Educator

04:38

Problem 10

Contrast and compare the mutagenic effects of deaminating agents, alkylating agents, and base analogs.

Dennis Howard

Numerade Educator

03:45

Problem 11

Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted?

Dennis Howard

Numerade Educator

01:14

Problem 12

Why are X rays more potent mutagens than UV radiation?

Madi Sousa

Numerade Educator

04:26

Problem 13

Contrast the various types of DNA repair mechanisms known to counteract the effects of UV radiation. What is the role of visible
light in repairing UV-induced mutations?

Niamat Khuda

Numerade Educator

05:11

Problem 14

Mammography is an accurate screening technique for the early detection of breast cancer in humans. Because this technique uses X rays diagnostically, it has been highly controversial. Can you explain why? What reasons justify the use of X rays for such a medical screening technique?

James Kiss

Numerade Educator

01:35

Problem 15

A significant number of mutations in the $H B B$ gene that cause human $\beta$ -thalassemia occur within introns or in upstream noncoding sequences. Explain why mutations in these regions often lead to severe disease, although they may not directly alter the coding regions of the gene.

Dennis Howard

Numerade Educator

02:46

Problem 16

Describe how the Ames test screens for potential environmental mutagens.Why is it thought that a compound that tests positively in the Ames test may also be carcinogenic?

Maryam Riaz

Numerade Educator

00:55

Problem 17

What genetic defects result in the disorder xeroderma pigmento$\operatorname{sum}(\mathrm{XP})$ in humans? How do these defects create the phenotypes associated with the disorder?

Gaurav Priyank

Numerade Educator

02:21

Problem 18

Compare DNA transposons and retrotransposons. What properties do they share?

Shiksha Dutta

Numerade Educator

01:30

Problem 19

In maize, a $D s$ or $A c$ transposon can alter the function of genes at or near the site of transposon insertion. It is possible for these elements to transpose away from their original insertion site, causing a reversion of the mutant phenotype. In some cases, however, even more severe phenotypes appear, due to events at or near the mutant allele. What might be happening to the transposon or the nearby gene to create more severe mutations?

Eric Goldman

Numerade Educator

01:04

Problem 20

It is estimated that about 0.2 percent of human mutations are due to TE insertions, and a much higher degree of mutational damage is known to occur in some other organisms. In what way might a TE insertion contribute positively to evolution?

Courtney Burson

Numerade Educator

03:49

Problem 21

In a bacterial culture in which all cells are unable to synthesize leucine (leu'), a potent mutagen is added, and the cells are allowed to undergo one round of replication. At that point, samples are taken, a series of dilutions are made, and the cells are plated on either minimal medium or minimal medium containing leucine. The first culture condition (minimal medium) allows the growth of only leut cells, while the second culture condition (minimal medium with leucine added) allows growth of all cells. The results of the experiment are as follows:
What is the rate of mutation at the locus associated with leucine
biosynthesis?

Sana Riaz

Numerade Educator

06:08

Problem 22

Presented here are hypothetical findings from studies of heterokaryons formed from seven human xeroderma pigmentosum cell
strains:
These data are measurements of the occurrence or nonoccurrence of unscheduled DNA synthesis in the fused heterokaryon. None of the strains alone shows any unscheduled DNA synthesis. Which strains fall into the same complementation groups? How many different groups are revealed based on these data? What can we conclude about the genetic basis of XP from these data?

Sana Riaz

Numerade Educator

01:16

Problem 23

Skin cancer carries a lifetime risk nearly equal to that of all other cancers combined. Following is a graph Imodified from
K. H. Kraemer (1997). Proc. Natl. Acad. Sci. (USA) 94:11-14] depicting the age of onset of skin cancers in patients with or without $\mathrm{XP}$, where the cumulative percentage of skin cancer is plotted against age. The non-XP curve is based on 29,757 cancers surveyed by the National Cancer Institute, and the curve representing those with $\mathrm{XP}$ is based on 63 skin cancers from the Xeroderma Pigmentosum Registry.
(a) Provide an overview of the information contained in the
graph.
(b) Explain why individuals with XP show such an early age
of onset.

Danielle Flores

Numerade Educator

01:58

Problem 24

It has been noted that most transposons in humans and other organisms are lacated in noncoding regions of the genome regions such as introns, pseudogenes, and stretches of particular types of repetitive DNA. There are several ways to interpret this observation. Describe two possible interpretations. Which interpretation do you favor? Why?

Dennis Howard

Numerade Educator

10:30

Problem 25

Mutations in the $I L 2 R G$ gene cause approximately 30 percent of severe combined immunodeficiency disorder (SCID) cases in humans. These mutations result in alterations to a protein component of cytokine receptors that are essential for proper development of the immune system. The $I L 2 R G$ gene is composed of eight exons and contains upstream and downstream sequences that are necessary for proper transcription and translation. Below are some of the mutations observed. For each, explain its likely influence on the $I L 2 R G$ gene product (assume its length to be 375 amino acids).
(a) Nonsense mutation in a coding region
(b) Insertion in exon 1 , causing frameshift
(c) Insertion in exon $7,$ causing frameshift
(d) Missense mutation
(e) Deletion in exon 2 , causing frameshift
(f) Deletion in exon 2 , in frame
(g) Large deletion covering exons 2 and 3

Ceyda Guley

Numerade Educator