Researchers have determined that 'junk DNA' which are large chunk's of an animal's genome that were once thought to be useless explain why snakes have 25 rows of ribs whereas a mouse only has 13. Scientists began discovering junk DNA sequences in the 1960's and believed it was simply DNA debris accumulated over the course of evolution; however, junk DNA has been found to serve important functions such as switching genes on and off and setting the timing for changes in DNA activity. Recently, scientists have discovered that noncoding DNA plays an important role in evolution. Since there is almost exactly the same number of ribs between the vertebrate species, scientists concluded that there must be some ways to alter expression of those genes regulating evolution to generate the massive amount of variation seen across the vertebrates.
A team of scientists led by biologist Moises Mallo turned to a mouse to research further. Most mice have 13 pairs of ribs, but there are some mutant mice that were bred to have 24 pairs of ribs just like snakes. The scientists traced the extra ribs to a mutation deactivating gene called GDF11 which stops other genes so that stem cells can morph back into many cell types. Without GDF11 slowing down the gene OCT4, the mice grew extra ribs and vertebrae. The OCT4 gene is similar in snakes, mice, and humans but the surrounding noncoding DNA looks different in snakes. To observe whether this junk DNA gives snakes a longer growth spurt, the team of scientists spliced noncoding snake DNA into normal mouse embryos near OCT4. The embryos grew large amounts of additional spinal cords indicating that junk DNA does play a factor in body shape regulation.
This was a very interesting article. As explained earlier, scientists began discovering junk DNA sequences in DNA in the 1960's. Recently however, they discovered that 'junk DNA' in fact does play a factor in body shape regulation. There are two genes that are responsible for the coding of ribs and vertebrae, and scientists were able to splice snake DNA with mouse embryos to determine how junk DNA is used in mice and snakes to create a backbone.