Genetics of organelles 2

Question 1

What are hetero- and homoplastic chloroplasts / mitochondria(?)

Answer 1

Due to poor regulation in chloroplasts / mitochondria(?), there can be unchecked deletions, duplications, insertions and inversions.

Heteroplasmic : The different chloroplasts host different genomes. There’s often big heteroplasmy between individuals, low heteroplasmy within a ingle individual.

Homoplasmic : The chloroplasts all host the same genome.

Question 2

What’s the current hypothesis regarding ow mitochondria are controlled that hey are proficient / compatible with the nuclear genome?

Answer 2

Mitochondria are inherited from the oocyte. The current hypothesis is that the oocytes are controlled by somatic cells in the ovaries. Mechanism unknown.

Question 3

Do human- and yeast mitochondria propagate in different ways?

Answer 3

Yes. Yeast mitochondria isn’t inherited from a maternal cell, they solely propagate through fusing / splitting. One mitochondrial allele encodes “petite mitochondria” which are respiratory deficient. Through mendelian inheritance and unfortunate fusing, a yeast cell can become fully respiratory deficient, which kills it.

Question 4

Name two mitochondrial factors which strongly correlate with aging.

Answer 4

1. GC content in the mitochondrial genome. More GC –> Longer life.
2. mtDNA damage correlates with age. Likely due to the oxidative environment which effects the mtDNA cumulatively.

Question 5

What’s cytoplasmatic male sterility?

Answer 5

Mitochondrial genes (which are maternally inherited) inhibit a male plant’s ability to form gametes.

Question 6

What’s the proposed origin story of the eukaryote cell?

Answer 6

Archaea - bacterial symbiosis. Mitochondria went from autonomous to non-autonomous as more as more genes were stored in a more safe location (the nucleus).

Reasons for moving DNA to the nucleus:
1. Nuclear DNA recombines in meiosis which buffers deleterious mutations. (Muller’s ratchet)
2. The mitochondria contain lots of ROS.
3. The regulatory machinery is better regulated.

Question 7

Since lots of mitochondrial genes are stored in the nucleus, why are there some left?

Answer 7

1. The mitochondrial genome is fast, it may be clumsy to transfer genes that may be required on the double to the nucleus.
2. The process may not be finished yet. The mitochondrial codons need to be translated into nuclear codons.