Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook

Sanders 3rd Edition

Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes

Problem 16

Chapter 17, Problem 16

A 50-year-old man has been diagnosed with MELAS syndrome. His wife is phenotypically normal, and there is no history of MELAS syndrome in either of their families. The couple is concerned about whether their children will develop the disease. As a genetic counselor, what will you tell them? Would your answer change if it were the mother who exhibited disease symptoms rather than the father?

Verified step by step guidance

Step 1: Understand the inheritance pattern of MELAS syndrome. MELAS (Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes) is caused by mutations in mitochondrial DNA (mtDNA). Mitochondrial DNA is inherited exclusively from the mother, as sperm do not contribute mitochondria to the zygote during fertilization.

Step 2: Analyze the scenario where the father has MELAS syndrome. Since mitochondrial DNA is inherited maternally, the father's condition does not affect the mitochondrial DNA of his children. Therefore, the children will not inherit MELAS syndrome from the father.

Step 3: Consider the scenario where the mother has MELAS syndrome. If the mother carries a mutation in her mitochondrial DNA, all of her children will inherit the mutated mitochondrial DNA, as mitochondrial inheritance is non-Mendelian and exclusively maternal.

Step 4: Explain the implications to the couple. If the mother is phenotypically normal, the children are not at risk of inheriting MELAS syndrome. However, if the mother exhibits symptoms of MELAS syndrome, genetic testing of her mitochondrial DNA can confirm whether the mutation is present and assess the risk for her children.

Step 5: Recommend genetic counseling and testing. If the mother is suspected to carry a mitochondrial mutation, further testing can provide clarity. Additionally, discuss reproductive options, such as mitochondrial replacement therapy, which can help prevent transmission of mitochondrial diseases.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

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

Mitochondrial Inheritance

MELAS syndrome is a mitochondrial disorder, meaning it is caused by mutations in mitochondrial DNA (mtDNA), which is inherited exclusively from the mother. This type of inheritance pattern is crucial for understanding the risk of passing on the condition, as only the mother can transmit mitochondrial mutations to her offspring.

Penetrance and Expressivity

Penetrance refers to the proportion of individuals with a specific genotype that actually express the associated phenotype, while expressivity describes the degree to which a genotype is expressed in an individual. In the case of MELAS, even if a child inherits a mutation, the severity and presence of symptoms can vary, making it important to discuss these concepts with the couple.

Risk Assessment in Genetic Counseling

In genetic counseling, assessing the risk of passing on genetic conditions involves evaluating family history, the mode of inheritance, and the specific genetic factors involved. If the father has MELAS, the risk to children is low, but if the mother were affected, the risk would be significant due to maternal inheritance patterns.

Recommended video:

Guided course

03:45

Descriptive Genetics

Related Practice

Textbook Question

You have isolated two petite mutants, pet1 and pet2, in Saccharomyces cerevisiae. When pet1 is mated with wild-type yeast, the haploid products following meiosis segregate 2:2 (wild type : petite). In contrast, when pet2 is mated with wild type, all haploid products following meiosis are wild type. To what class of petite mutations does each of these petite mutants belong? What types of progeny do you expect from a pet1 × pet2 mating?

Textbook Question

The first person in a family to exhibit Leber hereditary optic neuropathy (LHON) was II-3 in the pedigree shown below, and all of her children also exhibited the disease. Provide two possible explanations as to why II-3's mother (I-1) did not exhibit symptoms of LHON.

Textbook Question

Consider this human pedigree for a vision defect.

What is the most probable mode of inheritance of the disease? Identify any discrepancies between the pedigree and your proposed mode of transmission, and provide possible explanations for these exceptions.

views

Textbook Question

What is the most likely mode of inheritance for the trait depicted in the following human pedigree?

views

Textbook Question

The following pedigree shows a family in which several individuals exhibit symptoms of the mitochondrial disease MERRF. Two siblings (II-2 and II-5) approach you to inquire about whether their children will also be afflicted with MERRF. What do you tell them?

views

Textbook Question

You have isolated (1) a streptomycin-resistant mutant (strᴿ) of Chlamydomonas that maps to the chloroplast genome and (2) a hygromycin-resistant mutant (hygᴿ) of Chlamydomonas that maps to the mitochondrial genome. What types of progeny do you expect from the following reciprocal crosses?

mt⁺ strᴿ hygˢ× mt⁻ strˢ hygᴿ

mt⁺ strˢ hygᴿ× mt⁻ strᴿ hygSˢ

views