Lecture 17 Mitochondrial Inheritance and Disorders

Question 1

Endosymbiotic theory:

Answer 1

proposes that mitochondria and chloroplasts were once free-living bacteria

Question 2

How does the endosymbiotic theory help to explain some of the characteristics of
mitochondria and chloroplasts?

Answer 2

BOth organelles are similar to eubacteria, and DNA sequences found within them are also similar to eubacteria

Question 3

Explain uniparental inheritance of organelle-encoded traits

Answer 3

animal mtDNA inherited almost exclusively from female parent

Question 4

Heterosplasy:

Answer 4

the occurrence of two distinct varieties of DNA within the cytoplasm of a single cell

Arises through replicative segregation\Within a given eukaryotic cell, there can be thousands of copies of each type of organelle genome. Mutations that occur in one genome can give rise to populations of organelles that differ in DNA sequence within a cell

Question 5

Homoplasy:

Answer 5

The occurrence of one variety of DNA within the cytoplasm of a single cell

Question 6

Explain why many traits encoded by mtDNA and cpDNA exhibit considerable variation in
their expression, even among members of the same family.

Answer 6

During cytokinesis or cell
division, the process of replicative segregation separates the organelles randomly into the
daughter cells. In general, it is expected that equal proportions of organelles containing mutant
sequences and organelles containing wild-type sequences will be distributed to each progeny
cell. However, because replicative segregation is random, occasionally one progeny cell may
receive all wild-type organelles while the other progeny cell receives the mutant types.
Essentially, replicative segregation can lead to cells within a given individual and among family
members that differ in organelle phenotype and genotype.

Question 7

What evidence supports the endosymbiotic theory?

Answer 7

Perhaps the most convincing lines of evidence are sequence similarities of protein encoding and rRNA genes in mitochondria and chloroplasts to their respective homologous genes in specific groups of eubacteria. The mtDNA sequences are most similar to DNA from a group of bacteria called the α-proteobacteria, while the cpDNA sequences are most closely linked to the sequences from cyanobacteria4

Also antibiotic reactivity differences