You are currently browsing the tag archive for the ‘selfish’ tag.
VOLVOCINE ALGAE have a recent evolution of multicellularity, only 30-70 million years ago. This may produce a better record of the early history of this process than we have for other multicellular organisms. Metazoans and multicellular plants evolved over 550 million years ago (multicellular plants multiple times, and some suggest a very ancient history of multicellular algae over 800 million years ago). The fossil record for fungi is not very good, but unambiguous multicellular fungi were present by 500 million years ago. Bacteria meanwhile beat everyone out by evolving multicellularity several times perhaps 2-3 billion years ago. Since most multicellular organisms have a distant origin, extinction has eroded the base of their evolutionary trees so that the details of the transition are hard to extract. The volvocine algae have a much more recent history of multicellularity, and we have been able to determine much about their evolutionary history from phylogenetic studies of these algae and their relatives.
I HAVE ALREADY mentioned one type of selfish genetic element. These are mobile elements that can move about and reproduce within the genome, and include the transposon and retrotransposons. A second similar type of selfish genetic element are the homing endonucleases. These come in two forms, as introns which are spliced out of RNA and then translated into protein instead of being discarded, or as inteins that splice out of the protein once it has been synthesized. In both cases the homing endonuclease then during meiosis attacks the allele that does not contain the homing endonuclease intron or intein and triggers DNA repair that duplicates the homing endonuclease’s sequence. Since mobile elements and homing endonucleases either attack at a wide variety of sites or duplicate onto both of a pair of chromosomes, they are passed on according to Mendelian inheritance patterns. But there are other selfish genetic elements that are passed on preferentially, and a new paper in Genetica focuses on the effects of these selfish elements upon fertility in carrier males.