The Endosymbiont Hypothesis Can Explain Why We Have Two Very

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The Answer is It proposes that our two genomes originated when a type of aerobic prokaryotic cell was endocytosed by an anaerobic eukaryotic precursor cell, at a time when oxygen started to accumulate in significant quantities in the Earth's atmosphere. Over a long period, much of the original prokaryote genome was excised, causing a large decrease in its size, and the excised DNA was transferred to the genome of the engulfing cell. The latter genome increased in size and went on to undergo further changes in both size and form during evolution, developing into our nuclear genome; the much reduced prokaryotic genome gave rise to the mitochondrial genome.
The theory explains why mitochondria have their own ribosomes and their own protein-synthesizing machinery and why our mitochondrial DNA closely resembles in form a reduced (stripped-down) bacterial genome. Our current nuclear genome is much larger than that of the ancestral eukaryotic precursor cell because of mechanisms that copied existing DNA sequences and added them to the genome. After some considerable time, the copies acquired mutations to make them different from the parent sequences and led to the formation of new genes, new exons, and so on.

The Endosymbiont Hypothesis Can Explain Why We Have Two Very

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