Chapter 6--Survival of the Sickest

Edward Jenner, a country doctor in Gloucestershine, England, created the first vaccine in the end of the 18th century. He discovered that milk maids who had cowpox were immune to smallpox. Thus, he tested out his assumption by giving a harmless version of cowpox to a group of young boys. It turns out that they all were able to produce antibodies to protect themselves from smallpox. The first vaccine was then created.
   By creating the first vaccine, bioscientists found that genes could change. Each human beings starts off with exactly the same number of cells as the simplest form of bacteria, one single cell --- zygote. Inside of zygote has every single genetic instruction. These instructions carry 3 billion pairs of nucleotides (DNA base pairs) that have 30,000 genes. The genes of a person are organized in 23 pairs of chromosomes. One set of chromosomes comes from the mother, and the other set comes from the father. Yet, less than 3% of DNA contains instructions for building cells. The rest of DNA (about 97%) are noncoding DNA. Scientists changed the name of "Junk DNA" into noncoding DNA because the 97% of DNA are not directly involved in creating protein doesn't necessarily mean that it is junk, or non-usable. Later the author mentioned mitochondria, the microscopic workhorses. They function as powering plants, producing energy (called ATP) to run cells. They were mostly likely once independent, parasitic bacteria that evolved mutually beneficial relationship with some of pre-mammal evolutionary predecessors. They have their own inheritable DNA, mtDNA. Back to the point that genes could change, genetic changes are the product of accidental mutations caused by random and rare errors. Mutation happened when an error gets through and forms a new combination of DNA sequences( rearranging DNA). Mutations also occur when organisms are exposed to radiation or powerful chemicals. Outbreaks and pandemics are caused by either antigenic drift, which is when mutations occur in DNA of a virus, or antigenic shift, which is when a virus acquires new genes from a related strain.
    Last but not least, the author covered another topic, the "Jumping genes". In recent years, scientists have discovered that DNA can be modified in more ways that only by random mutations. In 1950's, Barbara McClintock discovered "jumping genes" --- whole sequence of DNA that moved from one place to another over times of environmental stress. She discovered this by observing the genetic of corn, in which the plants seemed to be undergoes a kind of intentional mutation. There are two types of "jumping genes"(transposons). The first one is DNA transposons, which perform a cut-and-paste process. The second one is DNA retrotransposons, which perform a copy-and-paste process. Moreover, large portions of our noncoding DNA/ Junk DNA are made of jumping genes. On the other hand, retroviruses are made of RNA, and can be written into DNA.