Exercises: Nuclear and Non-Nuclear Inheritance

Name two organelles in a eukaryotic cell that contain their own DNA, and state which kingdoms of organisms have each.

Distinguish between nuclear inheritance and non-nuclear inheritance.

In humans, mitochondria in the zygote are inherited almost entirely from one parent.

1. a) State which parent contributes the mitochondria.

1. b) Explain briefly why this is the case.

Mitochondrial DNA (mtDNA) is a small, circular, double-stranded molecule.

1. a) State two ways in which mtDNA differs from nuclear DNA in structure.

1. b) State one way in which the mtDNA is similar to the DNA of prokaryotes.

1. c) Explain how this similarity supports the endosymbiotic theory.

A mother from Galway has a rare disorder caused by a mutation in her mtDNA. She has two children, a son and a daughter, with a healthy father.

1. a) State whether each child is likely to inherit the mutation, giving a reason.

1. b) State whether the grandchildren of the daughter would be likely to inherit the mutation, and of the son, giving reasons.

1. c) Explain why the pattern of inheritance cannot be explained by Mendel's laws.

In some plants, leaves are variegated (patches of green and white). A mutation in chloroplast DNA causes white patches, where the chloroplasts cannot make chlorophyll. In a cross, the offspring always resemble the seed parent (the female parent) in leaf colour.

1. a) Explain this pattern of inheritance.

1. b) State why white tissue cannot survive on its own in a plant.

1. c) Name the process in the plant that is impaired in white patches.

Reciprocal crosses are carried out between two varieties of a plant: variety X (green leaves) and variety Y (variegated leaves, caused by a chloroplast mutation).

1. a) State the expected phenotype of the offspring when X is the female parent and Y is the male parent, and when Y is the female parent and X is the male parent.

1. b) Explain why the results of reciprocal crosses would be identical if the trait were controlled by a nuclear gene on an autosome.

1. c) Explain how reciprocal crosses can be used to distinguish nuclear from non-nuclear inheritance.

mtDNA is used in forensic science and in tracing maternal ancestry, for example in the identification of remains.

1. a) Explain why mtDNA can be used to trace maternal lineages over many generations.

1. b) Explain why mtDNA can sometimes be recovered from degraded samples when nuclear DNA cannot.

1. c) Explain one limitation of using mtDNA alone to identify an individual.

Mitochondrial replacement therapy (sometimes called "three-parent baby" techniques) replaces a mother's faulty mitochondria with healthy donor mitochondria.

1. a) Explain how this technique could prevent a child inheriting a mitochondrial disorder.

1. b) State which genetic information the child inherits from the donor and which from the parents.

1. c) Discuss one ethical issue raised by this technique.