The code for life is written exclusively in the language of DNA. It’s not a complicated molecule. It is made up of two long strands that have the bases that represent the code Guanine(G), Cytosine(C), Adenine(A), and Thymine(T) facing inward. The bases are held in the middle of the DNA strand by a “backbone” made of alternating Sugar molecules and Phosphate groups. The two strands stick together between C-G and A-T bases through weak Hydrogen Bonds.
These enormous molecules are used as the template to make a matching RNA copy, which is then read by ribosomes and tRNA molecules to manufacture a proteins with a specific Amino Acid sequence. Once the protein folds it is sent to the golgi apparatus where it is modified, glycosylated, then shipped out to its final destination in the cell. The amazing thing about DNA is that it is constantly being copied. As it is copied by the multi-protein complex called DNA Polymerase. This group of proteins are extremely good at copying the exact DNA code. DNA Polymerase even has a built-in proofreading step. However, mistakes/mutations are (D = 3) occasionally made. Mistakes are rare, in fact, the average rate of mutation is 1 in every 10 billion base pairs.
Most mutations do not affect us at all. Only about 2% of our genome actually codes for anything(proteins). If a mutation occurs in that 2%... inside a gene, it can result in a change in the protein it codes for. This change can have a wide range of effects. It is usually NOT beneficial for the organism. Every once in-a-while the mutation could actually help an organism to survive in the wild.
The inevitable mistakes made while copying DNA result in variability in a gene pool. It’s easy to see in humans, as none of us look exactly the same. Of course the exception to the rule is Identical Twins, who actually share the same DNA code and not surprisingly look nearly identical. Even when you look at a species that seems to have no variation like lady bugs, there is variation in the gene pool’s DNA. (C = 3) The variation means that some members of a population have traits that others don’t. Humans have known this for centuries. Ranchers and Farmers have used this to their benefit for ages by selecting the best offspring of a species to mate to keep the beneficial trait in the next generation. For example, Cauliflower, Broccoli, and Cabbage all were selected for their traits from the largely inedible Mustard plant. Dogs are another fantastic example. Wolves and dogs have an astonishingly similar Genome code, which isn’t a surprise as they were selected for by our human ancestors. More recently breeding dogs and selecting for sense of smell, pointing, and size has allowed humans to “Artificially Selected” for Blood Hounds, Poodles, Wiener dogs, Great Danes and every other breed of dog.
Domesticated animals of widely different species seem to share some common traits, including changes in body size, in fur coloration, in the timing of their reproductive cycle. Their hair or fur becomes wavy or curly and they have floppy ears. Drooping ears is a feature that does not ever occur in the wild, except for in elephants. And domesticated animals possess characteristic changes in behavior compared with their wild brethren, such as a willingness or even an eagerness to hang out with humans.
This ability of humans to “Select” for traits in a population of organisms was not fully understood until the work of Russian scientist Dmitri Belyaev. But Belyaev didn’t study dogs or wolves; his research focused instead on foxes. What might foxes be able to tell us about the domestication of dogs?
Dimitri was born in July 17th 1917 in Protasovo Russia. He was the 4th youngest son, looking up to his Geneticist big brother who was 18 years older. It was his brother’s influence that led him down the path of Genetics. Belyaev was a firm believer in Mendelian Genetics and began asking questions about the domestication of dogs. Belyaev and other Soviet-era biologists looked around at domesticated dogs, a species they knew had descended from wolves, and were puzzled. They could not figure out what process could account for the differences in anatomy, physiology, and behavior that they saw in dogs, but they knew that they could find the answers in the principles of mendelian genetics. Unfortunately during Stalinist Russia, political campaign against genetics called Lysenkoism banned its study. Biologists were unable to carry out the research necessary to investigate these questions.In 1948, genetics was officially declared a pseudoscience, resulting in the firing of all geneticists from their jobs.
It was in this political environment that Belyaev lost his job at the Department of Fur Animal Breeding at the Central Research Laboratory in Moscow, because of his commitment to classical genetics. Belyaev continued to discreetly study genetics. Eventually the overwhelming evidence supporting genetics led to it being accepted once again. Belyaev became of the director of the institute of cytology and genetics at the Russian Academy of Sciences in 1963, in Novosibirsk, Russia. Belyaev continue his work with Foxes, hypothesizing that the changes seen in domesticated animals could have been the result of selection of behavioral traits. More specifically, he believed that tameness was the critical factor. How likely was an animal to interact with humans?
He attempted to domesticate wild silver foxes. Belyaev and his colleagues bred them, with a strong selection for tameness. The foxes were tested for their reactions to an experimenter. The experimenter would attempt to pet and handle the fox while offering it food. If the fox bit the gloved hand or showed signs of aggression they were prevented from mating. The tamest were mated and the same selection was done in the next generation. Only those foxes that were least fearful and least aggressive were chosen for breeding. In each generation, less than 20 percent of individuals were allowed to breed.
The result of this breeding program conducted over more than 40 generations of silver foxes was a group of friendly, domesticated foxes. The domesticated foxes were more eager to hang out with humans, whimpered to attract attention, and sniffed and licked their caretakers. They wagged their tails when they were happy or excited. Further, their fear response to new people or objects was reduced, and they were more eager to explore new situations. Many of the domesticated foxes had floppy ears, short or curly tails, extended reproductive seasons, changes in fur coloration, and changes in the shape of their skulls, jaws, and teeth. Dimitri died in 1985. More than 50 years have passed since Belyaev began his silver fox breeding program, and research with these foxes continues today.
Belyaev showed that by “artificially selecting” for specific traits in a varied gene pool, fast and dramatic changes can occur to the resulting generations. This change over time is the same thing we see in “Natural Selection,” except that it’s not humans that choose who breeds.. It’s nature.
N40 AB.CDE W105 FG.HJK
A = Dimitri Belyaev was born in 19__7
B = The Soviet Union declared Mendelian Genetics to be wrong in 194__ , leading to its teachings being banned.
C =
D =
E = Belyaev became the director of the institute of cytology and genetics at the Russian Academy of Sciences in 19__3
F = In the Silver Fox experiment less than 2__ % of the population of the foxes were allowed to mate.
G = Only about ___% of our DNA actually codes for protein.
H = Belyaev’s Geneticist brother was __8 years older.
J = Belyaev died in 19__5
K =
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This Geocache was created and is maintained by Stanley Polley, a Science teacher at Loveland Classical Schools.