Researchers examined a family with an interesting distri...

Question

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

Person Condition Percent Mitochondria with
Mutation
Proband A and PN >90%
Brother A and PN >90%
Brother Asymptomatic 17%
Mother PN 86%
Maternal uncle PN 85%
Maternal cousin A and PN 90%
Maternal cousin A and PN 91%
Maternal Asymptomatic 56%
grandmother

How can some individuals in the same family show such variation in symptoms? What term, as related to organelle heredity, describes such variation?

Accepted Answer

Everyone. Let's look at the next question, Leigh syndrome can be inherited in various ways. It can be inherited when the mutated gene occurs on the X chromosome. This condition occurs more frequently in males than in females. What type of inheritance pattern is represented in this case, based on the epidemiological data presented. Well, Leigh Syndrome has the unusual characteristic of being caused by a mutation in one of more than 75 different genes and these genes are located in different places. So the mutation can occur in a gene on the autism of chromosomes on a sex chromosome or in mitochondrial d. n. a. Uh In this case it says that the mutated gene occurs on the X. Chromosome and the condition occurs more frequently in males than in females. So when you see that pattern occurring more frequently in males, it is a sex linked inheritance, which is choice see here, since males only have a single X chromosome, they only need to inherit one copy of the gene from their mothers to display the condition, whereas a female would need to inherit two copies of the gene and therefore is less likely to have the condition. So let's look through other answer choices to understand why they're not correct. Choice A is maternal inheritance. So it can be a little confusing to sort out maternal inheritance versus sex linked inheritance because sex linked traits are passed on from mother to son. But that's because the mother, the son has only a single X chromosome inherited from his mother. The Y chromosome is inherited from the father. So the inheritance goes from mother to son. But it's sex linked. Since the mutations on the sex chromosome, maternal inheritance refers to the fact that it could be only inherited from the mother. Because obviously in a sex linked trait in females they didn't have to inherit one allele from the mother and one from the father since they have two X chromosomes. So in that case you would inherit a gene from the father. A maternal inheritance on the other hand, is only inherited from the mother. It doesn't matter what the father's condition is since the father cannot pass it on and that occurs when the mutation is in the mitochondrial DNA. Since all of the mitochondria get all the mitochondrial DNA comes just from the mother. So that's the difference there. But maternal inheritance choice is not correct. Um You would not see any difference in males versus females inheriting the condition. They can only inherit from their mother but they would be equally likely to inherit. Choice. Beast has autism inheritance. Again, there that would be if the mutation was on the autism a chromosome and you wouldn't expect to see a difference in males versus females inheriting the condition, no difference in the sex inheritance. So that's why that's not correct. And then choice D mitochondrial inheritance. This would be the same as maternal inheritance since the mitochondrial DNA is inherited solely from the mother. So that's why Choice D isn't correct. So again, Leigh syndrome can be inherited in various ways can be inherited when the mutated gene occurs on the X chromosome, which would make this condition occur more frequently in males and females. What type of inheritance pattern is represented in this case, Choice C sex linked inheritance? See you in the next video.

Key Concepts

Mitochondrial Inheritance

Heteroplasmy

Penetrance and Expressivity

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