The genome of modern chloroplasts is roughly 50% of the size of the genome of the cyanobacterium from which it is thought to have been derived. In comparison, the genome of P. chromatophora's cyanelle is only slightly reduced relative to the size of the genome of the cyanobacterium from which it is thought to have been derived. What is a valid hypothesis that can be drawn from this comparison?
A) Lytic phage infections have targeted the chloroplast genome more often than the P. chromatophora genome.
B) P. chromatophora's cyanelle is the result of an evolutionarily recent endosymbiosis.
C) The genome of the chloroplast ancestor contained many more introns that could be lost without harm, compared to the cyanelle's genome.
D) All three of the hypotheses above are valid.
E) Only A and B are correct.

Question

Quizplus · Accepted Answer

The fact that the genome of P. chromatophora's cyanelle is only slightly reduced compared to its cyanobacterial ancestor suggests that the endosymbiosis that led to the formation of cyanelles is evolutionarily recent, whereas chloroplasts have had more time to undergo genome reduction.

The Genome of Modern Chloroplasts Is Roughly 50% of the Size