Question 1. (5 points) Many rare diseases are caused by deletion
of portions of the mitochondrial genome (mtDNA). These diseases
range in severity from relatively mild to extremely severe. For
example, progressive ophthalmoplegia causes muscle weakness that
typically appears in adulthood and does not significantly influence
lifespan. In contrast, other deletions cause Pearson syndrome,
which leads to severe anemia and pancreatic dysfunction and is
usually fatal in infancy. (Note that for the purposes of this
question, you do not need to know anything more about these
diseases than what is listed above.)

a. Give two reasons that could explain the variation in the
severity and symptoms of diseases associated with deletions of
mtDNA. (2 pts.)

b. Are the disease causing mtDNA mutations mentioned in above
likely to delete the mitochondrial origin of replication? (1
pt.)

c. Although these two syndromes are caused by mtDNA deletions,
they are not usually maternally inherited. For example, even the
mild disease, progressive ophthalmoplegia, is rarely passed from
mothers to offspring. What is the origin of non-maternally
inherited human mitochondrial diseases? Propose a molecular
explanation for why some diseases caused by mtDNA mutations do not
exhibit maternal inheritance patterns. (2 pts)