Skip to main content
Ch. 22 - Applications of Genetic Engineering and Biotechnology
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 22 - Applications of Genetic Engineering and BiotechnologyProblem 6
Chapter 22, Problem 6

A couple with European ancestry seeks genetic counseling before having children because of a history of cystic fibrosis (CF) in the husband's family. ASO testing for CF reveals that the husband is heterozygous for the Δ508 mutation and that the wife is heterozygous for the R117 mutation. You are the couple's genetic counselor. When consulting with you, they express their conviction that they are not at risk for having an affected child because they each carry different mutations and cannot have a child who is homozygous for either mutation. What would you say to them?

Verified step by step guidance
1
Explain the concept of compound heterozygosity: In cystic fibrosis (CF), a child can be affected if they inherit two different mutations in the CFTR gene, one from each parent. This is known as compound heterozygosity, where the child has two different defective alleles of the same gene.
Clarify the inheritance pattern: CF is an autosomal recessive disorder, meaning that a child must inherit one defective allele from each parent to be affected. The Δ508 mutation and the R117 mutation are both mutations in the CFTR gene, so they can combine to cause CF if inherited together.
Determine the probability of inheritance: Each parent has a 50% chance of passing on their respective mutation to their child. Use a Punnett square to calculate the likelihood of the child inheriting one mutation from each parent. Represent the alleles as follows: Δ508 (father's mutation), R117 (mother's mutation), and normal alleles (N).
Construct the Punnett square: Create a 2x2 grid where the father's alleles (Δ508 and N) are on one axis and the mother's alleles (R117 and N) are on the other axis. Fill in the grid to show all possible combinations of alleles the child could inherit.
Interpret the results: From the Punnett square, identify the probability of the child inheriting both the Δ508 and R117 mutations (compound heterozygosity). Explain that this combination would result in the child being affected by CF, despite the mutations being different. Emphasize the importance of understanding this risk and discuss potential next steps, such as further genetic testing or reproductive options.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
4m
Was this helpful?

Key Concepts

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

Cystic Fibrosis Genetics

Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the CFTR gene. For a child to be affected by CF, they must inherit two copies of the mutated gene, one from each parent. In this case, the husband and wife are both carriers of different CFTR mutations, which means they each have one normal and one mutated allele.
Recommended video:
Guided course
03:45
Descriptive Genetics

Heterozygosity and Carrier Status

Heterozygosity refers to having two different alleles at a gene locus. In this scenario, both parents are heterozygous for different CF mutations, meaning they are carriers but do not exhibit symptoms of the disease. However, being a carrier still poses a risk for their offspring, as they can pass on the mutated allele to their children.
Recommended video:
Guided course
02:48
Pedigree Symbols

Risk of Affected Offspring

The risk of having an affected child is determined by the combination of alleles inherited from both parents. Since the couple carries different mutations, there is a possibility that their child could inherit one mutated allele from each parent, leading to a child who is homozygous for a CF mutation. Therefore, it is essential to explain that while they may not share the same mutation, they still have a risk of having a child with cystic fibrosis.
Recommended video:
Guided course
06:59
RNA Interference
Related Practice
Textbook Question

Which of the examples of genetic testing below are prognostic tests? Which are diagnostic?

Individual sequencing (personal genomics) identifies a mutation associated with Alzheimer's disease.

Textbook Question

As genetic testing becomes widespread, medical records will contain the results of such testing. Who should have access to this information? Should employers, potential employers, or insurance companies be allowed to have this information? Would you favor or oppose having the government establish and maintain a central database containing the results of individuals' genome scans?

Textbook Question

One of the major causes of sickness, death, and economic loss in the cattle industry is Mannheimia haemolytica, which causes bovine pasteurellosis, or shipping fever. Noninvasive delivery of a vaccine using transgenic plants expressing immunogens would reduce labor costs and trauma to livestock. An early step toward developing an edible vaccine is to determine whether an injected version of an antigen (usually a derivative of the pathogen) is capable of stimulating the development of antibodies in a test organism. The following table assesses the ability of a transgenic portion of a toxin (Lkt) of M. haemolytica to stimulate development of specific antibodies in rabbits.

What general conclusion can you draw from the data?

Textbook Question

One of the major causes of sickness, death, and economic loss in the cattle industry is Mannheimia haemolytica, which causes bovine pasteurellosis, or shipping fever. Noninvasive delivery of a vaccine using transgenic plants expressing immunogens would reduce labor costs and trauma to livestock. An early step toward developing an edible vaccine is to determine whether an injected version of an antigen (usually a derivative of the pathogen) is capable of stimulating the development of antibodies in a test organism. The following table assesses the ability of a transgenic portion of a toxin (Lkt) of M. haemolytica to stimulate development of specific antibodies in rabbits.

With regards to development of a usable edible vaccine, what work remains to be done?

Textbook Question

Might it make sense someday to sequence every newborn's genome at the time of birth? What are the potential advantages and concerns of this approach?

Textbook Question

Sequencing the human genome, the development of microarray technology, and personal genomics promise to improve our understanding of normal and abnormal cell behavior. How are these approaches dramatically changing our understanding and treatment of complex diseases such as cancer?