Skip to main content
Pearson+ LogoPearson+ Logo
Ch. 14 - Gene Mutation, DNA Repair, and Transposition
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Not the one you use?Change textbook
All textbooksKlug 10th EditionCh. 14 - Gene Mutation, DNA Repair, and TranspositionProblem 23a
Chapter 14, Problem 23a

Skin cancer carries a lifetime risk nearly equal to that of all other cancers combined. Following is a graph [modified 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 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 XP is based on 63 skin cancers from the Xeroderma Pigmentosum Registry.
Provide an overview of the information contained in the graph. 
Graph showing earlier and higher cumulative skin cancer onset in XP patients versus later onset in non-XP individuals.

Verified step by step guidance
1
Step 1: Identify the two groups being compared in the graph: patients with Xeroderma Pigmentosum (XP) and patients without XP (the general population).
Step 2: Understand that the graph plots the cumulative percentage of skin cancer cases against age, showing how the risk accumulates over a lifetime for each group.
Step 3: Note the sample sizes for each group: 63 skin cancers from the XP registry and 29,757 cancers from the National Cancer Institute for the non-XP group, which affects the reliability and scale of the data.
Step 4: Observe the shape and position of the curves to compare the age of onset and rate of increase in skin cancer cases between the two groups, focusing on how early and how rapidly skin cancer develops in XP patients compared to non-XP individuals.
Step 5: Summarize that the graph illustrates a much earlier onset and higher cumulative risk of skin cancer in XP patients, highlighting the genetic susceptibility and the importance of DNA repair mechanisms in preventing skin cancer.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
1m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Xeroderma Pigmentosum (XP)

Xeroderma Pigmentosum is a rare genetic disorder characterized by a defect in nucleotide excision repair, leading to extreme sensitivity to ultraviolet (UV) light. Individuals with XP have a much higher risk of developing skin cancers at an early age due to their inability to repair UV-induced DNA damage effectively.

Cumulative Incidence and Age of Onset

Cumulative incidence represents the proportion of individuals who develop a condition over time. In the context of the graph, it shows the percentage of patients developing skin cancer by a certain age, allowing comparison of the timing and frequency of cancer onset between XP and non-XP populations.
Recommended video:
Guided course
08:18
Evolution

DNA Repair Mechanisms and Cancer Risk

DNA repair mechanisms, such as nucleotide excision repair, correct damage caused by environmental factors like UV radiation. Defects in these pathways, as seen in XP patients, lead to accumulation of mutations, increasing the risk and accelerating the onset of skin cancers compared to individuals with normal repair capacity.
Recommended video:
Guided course
05:44
Repair Pathways
Related Practice
Textbook Question

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?

442
views
Textbook Question

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 leu⁺ 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?

705
views
Textbook Question

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?

620
views
Textbook Question

Skin cancer carries a lifetime risk nearly equal to that of all other cancers combined. Following is a graph [modified 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 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 XP is based on 63 skin cancers from the Xeroderma Pigmentosum Registry.

Explain why individuals with XP show such an early age of onset.

491
views
Textbook Question

It has been noted that most transposons in humans and other organisms are located 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?

663
views
Textbook Question

Mutations in the IL2RG 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 IL2RG 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 IL2RG gene product (assume its length to be 375 amino acids).

Nonsense mutation in a coding region

641
views