Introductory Biology: Problem Three
Problem Title: Bloody Genes!
The Problem: The scientist Linus Pauling performed one of Biology's most imortant experiments. Pauling obtained blood samples from three different types of people. One of these people suffered from a disease called sickle-cell anemia. A second person did not herself have the disease but studies of her family lineage showed that she was a "carrier" for the disease and could pass it on to her offspring. The third person was entirely normal, which means that whatever gene caused the disease was not present in this person.
Question? Remembering that human beings are diploid organisms, can you explain how the above three people differed genetically with respect to the gene that caused sickle-cell anemia?
Pauling knew that a protein called hemoglobin carried oxygen in the blood and was the molecule that caused the red color of blood. Pauling performed a procedure called gel electrophoresis to analyze the hemoglobin from the blood of the three people.
Question? Can you briefly describe this procedure?
Gel electrophoresis can be done
to analyze either protein or nucleic acid molecules. Pauling was analyzing
a protein. The hemoglobin in the blood would move in a direction that reflected
the overall charge of the hemoglobin molecules.
Question? What result did Pauling
get when he looked to see how the three different hemoglobin molecules
moved in the gel?
Pauling's result was the first serious piece of evidence that connected a gene (that responsible for causing sickle-cell anemia) with the properties of a protein (hemoglobin).
Question? What was the conclusion that Pauling made and why did the gel results allow him to conclude this?
We can now sequence the DNA of genes, such as that which causes sickle-cell anemia, and identify the cause of the abnormal proteins made from the altered genes.
Question? What have we learned about the cause of sickle-cell anemia? What kinds of alleles (remember our discussion of mitosis and meiosis) for the hemoglobin gene did the three people that Pauling studied have?