Mendel .
lived in the middle of nowhere, so his work went widely unknown of until long after he had .
died. Mendel's ideas were expanded upon and refined, and they laid the groundwork for modern .
genetics. But mankind was not satisfied with knowing that there was a law of heredity, man .
wanted to delve deeper into it and find what exactly it was that made this work (The History .
of Modern Genetics par. 1). .
In 1869, Johann Friedrich Miescher discovered a slightly acidic chemical. He called the .
substance nucleic acid, because he found it in the nuclei of human white blood cells. .
Chemical analysis that was done in 1910 showed that there were two types of nucleic acid, .
called deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). In 1924, microscopic studies .
using stains for DNA and protein showed that they were both present in chromosomes. Some .
indirect evidence showed DNA to be related in some way to genetic material. Almost all .
somatic cells of any given species have the same amount of DNA, while the RNA content and .
the amount and kinds of proteins differed greatly between different cell types in the same .
species. DNA was not, however, at this time considered to be identical to genetic material, .
mostly because some chemical test had shown that DNA probably did not have the chemical .
diversity needed for a genetic substance. Proteins, however, are an extremely diverse .
collection of molecules. Thus, it was widely thought among scientists that proteins were the .
genetic material, and that DNA was just the structural framework of chromosomes. The .
actually identity of DNA and its relationship to genetic material was shown by an experiment .
done by Oswald Avery, Colin MacLeod, and Maclyn McCarty (Hartl 88).
Pneumonia is caused by Streptococcus pneumoniae, a bacterium that can synthesize a .
polysaccharide around itself. This ability allows it to be immune to the attacks upon it by .
the bacterial defenses in the body of the infected animal.