Laboratory Procedures and Important Historical Experiments - Genetics

In 1910, Thomas Hunt Morgan performed a test cross between white-eyed male Drosophila and homozygous red-eyed females to test the frequency of white eyes in the subsequent generations. The F1 generation all had red eyes, but when Morgan crossed the F1 generation, he noticed a 3:1 ratio of red to white eyes in the F2 generation. In all of his experimements, the white-eyed F2 flies were always male. Subsequent experiments supported the hypothesis that the white-eye trait was sex-linked (in this case, to the X chromosome).

This process is known as transformation. It was discovered after Griffith heat treated bacteria (to destroy their virulence) and noticed that mice injected with the heat-killed bacteria and a living, non-virulent strain would die of infection.

Hershey and Chase used radioisotopes to trace the DNA of a T2 phage (a virus that infects E. coli). Proteins contain sulfur; DNA does not. DNA contains phosphate; proteins do not. Using radioactive forms of sulfur and phosphate, they were able to selectively incorporate these isotopes into either the DNA or protein of a T2 phage and then physically separated the infected and uninfected bacteria. They found that the sulfur was not incorporated, while a portion of the phosphate entered the cells and could be recovered in the next generation. From these results, they were able to conclude that protein was not a hereditary material.

Miescher, a Swiss chemist, first identified "nuclein" in the nuclei of white blood cells. He noted that the substance contained higher levels of phosphorus than other proteins and was resistant to proteolysis. This discovery was not widely appreciated for over 50 years.

Levene accomplished all of these. He published more than 700 papers during his career. He used hydrolysis to break down and analyze yeast nucleic acids, proposing the composition of nucleic acids (phosphate, sugar, base) in 1919.

DNA microarray allows investigators to analyze gene expression on a large scale. A Northern blot only permits analysis of the expression of one (or several) genes at a time. PCR is a method of amplifying DNA and a Western blot allows for analysis of proteins.

The dispersive model (now recognized to be incorrect), proposed that every occurrence of DNA replication would create DNA hybrids (from fragments of the the original double helix) that are one part original and one part new DNA. Each additional round would produce double helices with greater and greater quantities of DNA.

One strain of Pneumococcus was called smooth due to a protective capsule, and the other strain that lacked the capsule was called rough. Mice that were injected with the smooth strain died, and mice injected with the rough strain lived because their immune system killed the bacteria. Griffith also killed some of the smooth strain and found that when mice were injected with the dead smooth strain lived, but mice injected with both live rough strain and dead smooth strain died. He determined that the living smooth strain cells were being transformed by some material from the dead smooth strain. Later experiments proved this material to be DNA.

Polymerase chain reaction (PCR) is a method by which a specific sequence of DNA can be copied and replicated many times over in a test tube, which has been of enormous importance to the field of molecular biology. The other techniques listed all are important in molecular biology as well, but are typically for detection or other manipulations, not replication.

Watson and Crick crystallized DNA to be able to visualize the structure, and it was this finding that led them to propose the double helix. Fun fact: Rosalind Franklin's work was essential to this finding as she was the expert in x-ray crystallography, but Watson and Crick are traditionally given all the credit.

It was Gregor Mendel who did studies on pea plants to first described the concepts behind genetic inheritance. By breeding pea plants with different visible phenotypes and observing the phenotypes of the offspring produced, he was the first scientist to provide rules for heredity (now known as Mendelian inheritance).

The question is asking about separating mRNA fragments, not DNA fragments. Hence, the only procedure applicable is Northern blot. Southern blot is used for DNA, and Western blot is used for protein. In addition, there is no such thing as an Eastern blot.

The experiment performed by Hershey and Chase showed that bacteriophages insert their DNA into bacteria, and not their protein. This demonstrated that DNA is the genetic material, and not proteins. Law of independent assortment and segregation are both Mendelian concepts.

Gregor Mendel was a German friar who lived in the mid- to late-nineteenth century. He conducted a years-long series of experiments using pea plants in which he carefully tracked each plant's physical traits and determined how cross-fertilization (breeding the pea plant to another pea plant, rather than to itself) affected the plants' offspring. Seed color, flower shape, height, and pod shape were among the traits he studied. In the end, he summarized his work into three laws of heredity: the laws of segregation, independent assortment, and dominance. He also coined the terms "recessive" and "dominant," in reference to genetic traits.

Unfortunately, Mendel's work remained largely unacknowledged through his life. The importance of his studies was only recognized by other scientists decades after his death.