Sunday, March 29, 2009

Fossil Genes

On page 134, Rebecca Zufall and Mark Rausher showed that I. quamoclit has degenerated its pathway for making blue and purple. Why is this? Compare I. quamoclit to M. leprae (132) and discuss what happened to each. How does M. leprae relate to the “use it or lose it” rule (pg. 132)?
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2 comments:

  1. Katie FMarch 30, 2009 at 8:13 AM

    The relaxation of the blue and purple genes in the I. quamoclit is due to a mutation in the blue/purple pathway and instead results in the synthesis of red pigments. The blue and purple coloration attracts bees and is a selective advantage for pollination by these insects. The red pigmentation, on the other hand, attracts hummingbirds, thus, instead of bees, I. quamoclit is pollinated by these hummingbirds. Since the blue/purple pigmentation is no longer used in the plant, the genes that code for its production have been fossilized and no longer work.
    This is similar to what happened with M. leprae, the pathogen responsible for leprosy. This microbe has around 1100 fossil genes, more than any other known organism. This is attributed to the highly specific lifestyle of M. leprae. It can only llive within its host cells and its highly dependent on its host’s metabolic pathways. It allows it host’s genes to do the majority of the work and therefore has no need for its own genes. Because of this, natural selection does not actively maintain these genes that can be accounted for by the hosts and over tine M. leprae loses these functional genes. This is a perfect example of Carroll’s “use it or lose it” principle because it demonstrates how organisms lose proper coding for genes they do not use. This occurs gradually as mutations in these genes occur and then are not fixed. The organism no longer uses the gene so any mutations go unnoticed as they do not affect the survival of the organism.

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  2. Kimberly KenyonApril 12, 2009 at 7:32 PM

    Carroll discusses that the red color for the morning glories is adaptive. Meaning it occurred due to its environment or factors that required the plant to adapt to in order to survive. He also discusses that the fossilization of the blue/purple color is due to relaxed selection on genes. Relaxed selection is when a gene is relaxed and not used it eventually becomes less functional or it eventually becomes fossilized.

    The production of the color for the morning glory is determined in an enzymatic pathway, where different enzymes will create the blue, purple, or red pigments. In red flowers the blue and purple enzymes are impaired or altered so they no longer contribute to the color of the flower. Small alternations in the enzymes could have been caused by mutations as well as the “Use it or Lose it” rule. The more red pigment the flowers used the less blue/purple they used. The blue/purple eventually got altered and fossilized.

    In areas with many bees the blue/purple Ipomoea would be blue/purple and attract the bees in order to be pollinated and reproduce. In areas with many hummingbirds, the red color of I. quamoclit would be present and the hummingbirds would pollinate the lowers to help them reproduce. The red color was noted as a selective advantage in certain areas that contained hummingbirds. The red color attracted hummingbirds and the blue/purple color attracted bees.

    The pathogen M. leprae is similar to the events that occurred with Ipomoea. M. leprae lives inside its host cell and depends on it greatly. It relies on its host’s genes to do the work, meaning it does not need its own genes. Many genes in the pathogen are, therefore, fossilized. This is a great example of the “Use it or Lose it” rule because the pathogen relied so much on its host that over time most of its genes are fossilized and no longer function. Mutations and other problems in the pathogen are ignored because the genes are no longer used.

    http://www.nsf.gov/news/news_summ.jsp?cntn_id=100369 http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.1833

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