Evidence for Evolution Double endosymbionts Chloroplasts and mitochondria are organelles within eukaryotic cells (cells of organisms other than bacteria, which do not have organelles). These organelles have their own genetic material. It has been shown previously that organellar DNA is much more similar to bacteria than to nuclear DNA from eukaryotes. This, and other evidence, led scientists to the now widely held belief that these organelles were once free-living prokaryotic cells that began living in proto-eukaryotic cells and eventually the two types of cells required each others presence for existence. They were obligate endosymbionts. It's worth noting that organelles still reproduce autonomously within eukaryotic cells. Recently, a paper in Nature provided evidence for a double endosymbiotic event in cryptomonad algae. Several lines of evidence led researchers to conclude this double event had taken place. First, most chloroplasts are double-membraned (one membrane from the protoeukaryotic cell,
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