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

Develop a pedigree that summarizes the information presented in the table.

Accepted Answer

Welcome back. Here's our next question. Leigh syndrome can be inherited in various ways. It can be inherited when both copies of the gene in the cell bear the mutations. This can affect the offspring. Both male and female. Despite having parents who do not show signs and symptoms of the condition. What type of inheritance pattern is represented in this case? So when we see that we need two copies of the gene to be mutated we have males and females affected equally. And you see skipped generations. So offspring affected when parents are not, this type of inheritance will be autism. A while recessive autism all chromosomes of course we have two of each type. And so therefore in an autism over decisive condition you need two copies of the mutant alittle one on each chromosome, males and females will be affected equally. Since it doesn't affect the sex chromosomes. And you can see skip generations because individuals could be carriers where they have just one affected copy. But since they have one unaffected copy they don't have the condition. So with that in mind let's look over our answer choices and we do see that choice. See here is autism inheritance which is what we have specifically autism recessive. Let's just look at our other answer choices. Choice A. Is mitochondrial inheritance. That would be if the mutated gene was carried on the mitochondrial D. N. A. But there we would see just a maternal pattern of inheritance inherited only from the mother. You'd see male and female offspring is affected equally since it's in the mitochondrial DNA but only inherited from an infected mother affected father could not pass that on since all mitochondrial DNA comes from the mother. So that's why Choice A. Is incorrect. Choice B is paternal inheritance and this is not correct either. Um Paternal inheritance would be very rare because it would mean something would have to be on the Y chromosome. You would see it only passed from father to son and you would never see any females being affected. But this is not the case here obviously and enjoys the sex linked inheritance. Um When the mutation would be on the X. Chromosome or it could be on the Y chromosome. But again that would be very unusual. And you'd see a paternal inheritance pattern there on the X chromosome. You'd see males be affected far more frequently than females. Since males have only a single X chromosome, they would only need one copy of the mutated gene to have the condition where the female would need two copies. So let's cross that off. Um And again, unusual thing about Leigh syndrome is that it can be caused by mutations in one of 75 different genes. Since it affects the mitochondria, the proteins that make up the complexes that perform oxidative phosphor relation in the mitochondria. So it can have this is such a big system different proteins. It can be caused by a mutation one of about 75 different genes. So those genes can be located on the autism of chromosomes, the sex chromosomes or the mitochondrial D. N. A. Uh So that means there's different patterns of inheritance, even though it's the same syndrome in this case, when we see that it's inherited when both copies of the genes in the cell mutations affects both male and female offspring and affects offspring whose parents do not show the condition. What type of inheritance pattern is this choice? See autism. All inheritance. See you in the next video.

Key Concepts

Mitochondrial Inheritance

Leigh Syndrome

Pedigree Analysis

Watch next