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Mutants in our Midst How Mutations may Affect the Skeletal and Musculature Development of Frogs
The Body • Anatomy is the structure and arrangement of the body parts of an organism • Anatomical traits are very similar within a species and within related members • These similarities may extend to other species • Dogs vs. Wolves, Deer vs Antelopes • Our anatomy is strongly influenced by the genes we inherit from our parents • Genes are DNA sections that encode information
DNA • DNA is used by all known organisms to store the information required to continue living • Genes are “recipes” encoded by the specific sequence of the 4 DNA bases (A, G, C, T) that tell the body how to make essential proteins • Think of the 4 bases as an elaborate Morse code! • Every single cell in your body has the same DNA as every other cell, but different genes may be turned on or off
The Body… • Sometimes there are problems with the development of the body that result in what scientists call anatomical mutations. • Before discussing mutations, however, we should get some background on the body in general.
Anatomy • Take a look at the skeletal structure of a human and compare it to the frog skeleton. • How are they similar? How are they different?
Humans vs. Frogs • The most apparent difference when you look at the two skeletons might be that the frog seems to have much longer legs for its body size than the human. • Each species has a typical set of ratio of bone lengths that give the characteristic appearances of the body.
Why the Difference? • Why do you think that frogs have such long back legs? • What purpose could their legs serve that humans don’t need? • What benefit would it be to have hind legs that were much larger than our upper body?
Movin’ and Shakin’ • Frogs do not walk, they jump; therefore, they must have enough force to propel their body forward and up • Humans and other walkers need only the strength to balance their weight on one leg (if biped, and two legs if quadruped) while lifting and extending the other. • This very different requirement for motion is what causes the frog’s anatomy to be so different in the hind legs.
Alert! MUTATIONS AHEAD! • In 1995, a group of Minnesota students discovered something that shook the ecological world—the gross malformations of frogs. • The students found very few frogs in areas that were once heavily populated with amphibians, and the frogs they did find had mutations like extra or missing limbs, improperly placed eyes and mouths, or malformed spines. • What had happened???
Searching for Answers • Ecologists and other scientists found that mutation among amphibians was increasing worldwide, as was the decline in amphibian populations. • What exactly was happening to these frogs? • What effects did these mutations have on the individual frog? On the ecosystem?
What happens when something goes wrong • Frogs and other amphibians, due to their development cycle, are often found with mutations as adults. • A mutation may be as simple as extra toes, or as serious as having an extra pelvis and two extra legs. • What causes these mutations?
Frog Life Cycle • Frogs and other amphibians are very vulnerable to environmental factors that can cause mutations because they constantly undergo anatomical change during the first part of their life.
Causes of Mutations • Much speculation surrounds the exact causes of the mutations in amphibians. • One known cause is the trematode parasite Ribeiroia ondatra. • The trematode population has grown due to rising temperatures and increased contamination • Chemical pollutants – Polluted water run-off from factories and cities? • Overexposure to UV radiation due to a depleted ozone layer? • What do you think?
How a Mutation Affects the Skeleton • Chemicals that are absorbed during the development stage will cause a significant change in the frog’s DNA that will create a mutation. • Parasites infect tadpoles and alter DNA during limb formation, causing missing limbs, extra limbs or other problems. • Most mutations deal with the skeletal system. • Examine the frogs to the left. • The top frog has a malformed hip and only one leg. • The middle frog has an underdeveloped leg. Note the fused and bent bone of the right leg. • The final frog has multiple bones in the left leg. It has two femurs and five bones in the lower leg. The joints are improperly formed and therefore the limb is immobile.
Why isn’t having more legs beneficial? Amphibian Malformation Pictures • You would think that having multiple legs would help the frogs jump better or that having more bones would provide better leg strength, but this unfortunately is not the case. • The extra bones disrupt the proper leverage that the normal bones would provide. • Extra limbs offset the natural balance and movement of the frog and are generally nonfunctional.
The Future of Frogs • Many scientists have said that frogs and other amphibians are indicator or sentinel species for environmental changes—they are the proverbial canary in the mineshaft. • Since frogs live the first half of their lives in the water they are extra-sensitive to changes in the water’s quality and overall changes in the environment. • Many ecologists suggest that the same environmental changes that are causing gross frog mutations may eventually cause harmful health effects in the human population.