1. Identify as many different signals as you can that are present in and around a typical eukaryotic protein coding gene in addition to the actual coding sequence. Briefly explain what each of these signals does.
2. Sickle cell anemia is an inherited disease that is particularly prevalent in individuals with Central African ancestry.
a. What is the nature of the genetic defect responsible for sickle cell anemia.
b. How is that defect manifested at the protein level.
c. How does the genetic defect cause the shape change of red blood cells and cause the other symptoms characteristic of sickle cell anemia.
d. What mechanism has prevented the sickle cell gene from being reduced to a very low level in the population by early death of afflicted individuals. To find the answer for this question, you will need to look at the lecture notes (or text pages 566-567, which you will find difficult to follow without some background explanation).
e. The symptoms of sickle cell anemia tend to become worse when the blood is under oxygenated. What is believed to be the reason for this.
3. Describe two very different mechanisms that can result in beta-thalassemia. (With a little creative effort, you should be able to come up with far more than the two that were identified in the textbook and in the notes).
4. Describe as many different ways as you can in which mutations that are not contained within the protein coding sequence of a gene can alter its level of expression (hint: the answers are spread over several chapters of the textbook)
5. What was the earliest evidence suggesting the possibility of a one gene - one enzyme relationship. Roughly when was this evidence obtained?
6. Describe the interactions that allow an eye imaginal disc from a larval Drosophila with the vermillion eye mutation to form normal pigment when allowed to undergo metamorphosis in the abdomen of a larva with the cinnamon eye mutation.
7. Explain why the opposite experiment does not work (a cinnebar eye disc in a vermillion larva).
8. What is an auxotrophic mutation?
9. A collection of auxotrophic strains of Neurospora that all require tryptophan for growth has been found to involve mutations at a number of different genetic loci. Explain how mutations in different genes can lead to the same auxotrophic growth requirement.
10. If you know the biosynthetic pathway for a particular nutrient, how would you determine which steps had been lost in individual mutant strains selected randomly from a collection of strains that are auxotrophic for the nutrient in question.
11. Propose a procedure for using auxotrophic mutants to determine the order of the blocked steps in a biosynthetic pathway whose details you did not know.
12. Explain the concept of genetic complementation as it applies to the individual steps in a metabolic pathway.
13. How can a wide range of variability, such as human hair color, be achieved genetically?
14. In an early study on arginine auxotrophs, Beadle and Tatum found that some of the strains would grow when supplied with any of arginine, ornithine or citrulline. Others could not be grown with ornithine, but would grow with arginine or citrulline. Still others could only be grown with arginine, and not with citrulline or ornithine. What did this tell them about the relationship of arginine, ornithine and citrulline to one another?
15. Fusion of an auxotrophic strain of Neurospora that requires either arginine or citrulline to grow with another auxotrophic stain that can be grown with any of ornithine, citrulline or arginine generates a heterokaryon strain that can be grown in a minimal medium that does not contain arginine, citrulline or ornithine. Construct a diagram to illustrate how such growth can occur. What is the genetic phenomenon that is involved called?
16. This question requires a speculative approach that goes beyond the material actually covered in the lecture and the notes. You have a collection of auxotrophic mutations in Neurospora that all require the same nutrient. How would you determine how many different genes with loss of function mutations are represented in the collection. Neurospora is haploid in the vegetative phase. For purposes of this question assume that complementation never occurs between two mutations in the same gene (we will see later that there are rare exceptions to that rule). Do not use any methods that require the formation of diploid nuclei, meiosis, independent assortment, or genetic recombination.
Go to Review Questions for the Following Lecture
Return to Index of Review Questions
Go to Review Questions for the Previous Lecture
Return to Lecture 8