Lecture 18

Question 1

Why is 16S rRNA the best molecule for determining evolutionary relationships between cellular species?

Answer 1

It is universal (all cells encode it), conserved (evolves slowly), long (provides many characters to compare), and does not tend to be transferred horizontally.

Question 2

What evidence supports the endosymbiotic origin of mitochondria and chloroplasts?

Answer 2

They are about the same size as bacteria and replicate independently.
Both contain their own circular genomes of bacterial genes.
Both contain bacterial ribosomes.
Their 16S rRNA is most closely related to that of bacteria.
Antibiotics that inhibit bacterial ribosome function also inhibit organelle ribosome function.