Question

The pedigree below shows the inheritance of a dominant allele of a gene in a family over several generation. Circles represent females and squares represent males. Shaded symbols indicate individuals carrying the allele. The pedigree suggest that the gene is on a nuclear chromosome, and not on a mitochondrial DNA, because A) mitochondrial genes are not heritable B) mitochondrial mutations cannot produce dominant traits C) maternal mitochondrial mutations are inherited by all of a mother's offspring D) mitochondrial DNA is circular, whereas chromosomal DNA is linear

Answer 1

Complete question:

You will find the pedigree in the attached files

Answer:

The correct option is C) maternal mitochondrial mutations are inherited by all of a mother's offspring.

Explanation:  

Mitochondrial inheritance is one of the ways in which a disease or a trait might be inherited from the maternal line.

Most of the DNI is located in the nucleus, but there is also DNI in mitochondria. Sperm cells hardly carry mitochondria, so mitochondrial DNI is mostly inherited from the maternal side. If there exists any mutation in this DNI, the whole progeny of the mutated woman will be affected, as they will get the mother´s mitochondria carrying the mutation. On the contrary, if there is a man affected by a disease caused by a mutation in mitochondrial DNI, non of their descendants will get the disease.

In the exposed pedigree, we can see that the mother is affected by the disease, but the couple had two daughters, and only one of them was affected, while the other one was not. This tells us that the mutation occurred on a nuclear chromosome. If the mutated allele was in mitochondria, both daughters would be affected.