CHAPTER VI: JUMP INTO THE GENE POOL

Edward Jenner was just a country doctor until he discovered that the cowpox which Milkmaids caught, were resistant to small pox, a very deadly infection in humans. He scraped the cowpox sore off a Milkmaid and infected several teenage boys as an experiment to prove his hypothesis, and he was right--the cowpox infection resulted in the protection from smallpox. Edward Jenner became the first man to discover vaccination. The word vaccine comes from the Latin word for cow, vacca, and the Latin name for cowpox, vaccinia.

Vaccines are the relatively harmless version of the virus we want to vaccinate against. It is harmless in the sense that it is weakened or killed and broken up into pieces, or, like cowpox, a relative close enough to the harmful virus that our bodies will recognize it, but distant enough that ti does not cause a serious disease). By introducing the harmless virus to our bodies, we stimulate our immune systems to produce the antibodies that defend against that virus. Without having the right-fitting, performed anti-bodies, viral attackers can make us sick before our immune system has time to generate the antibodies we need to fight back.

Every human being starts off with one cell, the zygote, which is the product of a sperm cell supplied by the father and an egg cell supplied by the mother. These union of cells combine to produce a human. The first cells contains every single genetic instruction to manufacture the proteins used to build a human being. Those instructions are carried in about 3 billion pairs of nucleotides called DNA base pairs. There are assumed to be less than 30,000 genes which are organized among twenty-three pairs of chromosomes for a total of forty-six. One set of twenty-three chromosomes comes from the mother and the other from the father. Every pair except for the twenty-third --the sex chromosomes--is a matched pair. In other words, each chromosome carries the same type of instructions, although they will vary greatly in how they instruct your body to carry out those instructions.

Usually, with one very important exception, every cell in your body contains the same DNA--two complete sets of chromosomes with all the genes containing all the instructions you need to build every type of protein and every type of cell. The exception is germ cells, the cells that combine to produce offspring. However, less than 3 percent of your DNA contains instructions for building cells. The vast 97% of it isn't active in building anything. Scientists initially called this additional genetic material "junk DNA"  because they thought that this DNA did nothing. However, it turns out that the massive volume of genetic information in this portion of our genome may play a critical role in evolution. What was once called junk DNA is now called noncoding DNA, which means that it isn't directly responsible for making proteins.

• Mitochondria have their own inheritable DNA called mitochondrial DNA or mtDNA. 
• Evolution hasn't only been shaped by adaption to viruses and bacteria--it's probably been shaped by integration of viruses and bacteria.
• Mutations happen when DNA is copied from the "parent" cell to the "daughter" cell. This process usually produces accurate copies, but errors in the production of the long string of information that produces DNA does occur. This copying process is usually "proofread" with phenomenally low error rates--one out-of-place nucleotide in every billion copies.
• Mutations also occur when an organism is exposed to radiation or powerful chemicals (like those found in cigarette smoke and other carcinogen). When this happens, it can also rearrange DNA.
• Outbreaks and pandemics are thought to be caused by antigenic drift, when a mutation occurs in the DNA of a virus, or antigenic shift, when a virus acquires new genes from a related strain.
• Scientists begin to conceive genes as an intricate network of information with an overall regulatory structure that can react to change. I.e.: When scientists isolated specific genes related to specific functions, other genes stepped up and filled in for their KOed colleague (in other words, removing the gene essentially did nothing). The whole system is interconnected and automatically covers for its parts.
• Barbara McClintock produced evidence that in certain circumstances, parts of the genome actively triggered much larger changes. Today, the genetic nomads McClintock discovered are called jumping genes or transposons. Sometimes these jumping genes copy and paste--copying themselves and then inserting the new material elsewhere in the genome while remaining in the original location. Other times they cut and paste--removing themselves from their starting place and inserting themselves somewhere else. Jumps are genomic responses to internal or environmental stress that cells can't handle under their existing setup. When that happens, the proofreading mechanism is suppressed and mutations are allowed to blossom. Jumping genes also tended to jump to certain genes more than others. McClintock believed that the genome directed its jumpers toward those places in the genome where mutations were most likely to have a beneficial effect.
• E.coli is a digestive workhorse in humans.
• Barry Hall believes that hypermutation helped the bacteria to produce the mutations they needed to survive about 100 million times faster than the mutations otherwise would have been produced.

Rachel Putri Utomo
Block F, Honors Biology
Mr. Kevin Quick
Academic Year 2013-2014