The Chapter begins with the history of cowpox and how Edward Jenner invented vaccines as he found out that people who caught cowpox were resistant to small pox. Every human starts of from being 1 bacteria and duplicates millions of times to get to our form and shape now. Our DNA consists of 3 billions different nucleotides and every human has 23 chromosomes from each one of their parents, these are called the sex chromosomes adding up to a total of 46. These chromosomes determine our characteristics.
Scientists originally believed that only accidental mutations can possibly cause genetic changes. They thought pandemics followed a trend with sun spots, but they later realized it was because of the antigenic drift that caused our body to be vulnerable. Babara McClintock discovers the "jumping genes" and proposes that genetic changes does not necessarily have to be accidental. She puts an example of how corn's DNA migrates. John Cairns also did an experiment to prove that digestive bacteria can mutate to be not lactose tolerant when only fed lactose. Proving that genetic changes can happen intentionally.
Finally, only 3% of our DNA are used for coding sequences.And scientists found out that the rest are actually a lot of "jumping genes" instead of "junk sequences". Moreover, the Weissmann barrier distinguishes germ cells and somatic cells as changes of somatic cells cannot be passed on.
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