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? 

Verified step by step guidance

1. Analyze the pedigree chart: MERRF (Myoclonic Epilepsy with Ragged Red Fibers) is a mitochondrial disease, which means it is inherited through mitochondrial DNA. Mitochondrial DNA is passed exclusively from mother to offspring, as sperm do not contribute mitochondria during fertilization.
2. Identify affected individuals: In the pedigree, individuals with filled symbols (black circles or squares) exhibit symptoms of MERRF. Note that all affected individuals are descendants of the female in generation I-1, who is also affected.
3. Determine inheritance pattern: Since mitochondrial DNA is maternally inherited, only females can pass the disease to their offspring. Males, even if affected, cannot transmit the disease to their children.
4. Focus on II-2 and II-5: Individual II-2 is female and affected, meaning she has a high likelihood of passing MERRF to all her children, regardless of their sex. Individual II-5 is male and affected, but he cannot pass the disease to his children.
5. Explain the implications: Inform II-2 that her children are at risk of inheriting MERRF due to maternal mitochondrial inheritance. Inform II-5 that his children will not inherit MERRF, as mitochondrial DNA is not transmitted through males.

Key Concepts

Mitochondrial Inheritance

Mitochondrial inheritance refers to the transmission of genetic traits through mitochondrial DNA, which is inherited exclusively from the mother. This means that only females can pass on mitochondrial diseases to their offspring. In the case of MERRF (Myoclonic Epilepsy with Ragged Red Fibers), if a mother is affected, all of her children may inherit the condition, while the father does not contribute to the mitochondrial DNA.

Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance patterns of traits or diseases within a family over generations. In a pedigree chart, males are represented by squares and females by circles, with filled shapes indicating affected individuals. By analyzing the pedigree, one can determine the likelihood of offspring inheriting a genetic condition based on the affected individuals in previous generations.

Risk Assessment for Offspring

Risk assessment for offspring involves evaluating the probability that children will inherit a genetic condition based on parental genotypes. In the case of mitochondrial diseases like MERRF, if the mother is affected, there is a 100% chance that her children will inherit the mitochondrial DNA, and thus the potential for the disease. The father's genetic contribution does not affect the risk of mitochondrial diseases.