Common plasmids are simple DNA molecules which contain a few genes and regulatory elements. Most viral genomes are more complex. For example, the genome of phage lambda contains approximately 50 genes. About 4,000 genes are present in the E. coli genome while there is approximately 1,000 times more DNA in the genome of a mammal. This progression in genome complexity is the topic of this exercise. Here, students compare the electrophoretic patterns of restriction digests of a plasmid, phage lambda DNA, and cow DNA from thymus and kidney as shown in the figure below.
DNA fingerprinting relies on the fact that DNA can be extremely variable in sequence from one individual to another and from one organism to another. Thus, the method has been used to identify individuals in forensic and paternity cases and to study genetic lineages of closely related organisms. These applications are discussed in the text and the latter application is illustrated in this experiment. In the exercise, students are given two DNA samples which are identified in the instructor guide. One sample is from sheep and the other from cow.
This exercise was designed to provide an exciting introduction to specific gene structure and function. In the experiment, students are given two plasmids (A and B) which are identified in the instructors guide. One plasmid (A) has a functional gene for the enzyme ß-galactosidase. The ß-galactosidase gene in the other plasmid (B) is inactive because it contains a segment of foreign DNA. In the first part of the exercise, students analyze restriction digests of both plasmids in order to determine which plasmid should have a functional ß-galactosidase gene.
Many changes in the structure of hemoglobin have arisen by mutations. About one person in 100 carries a mutant hemoglobin gene, and these individuals have abnormal hemoglobin molecules in their blood. One of the most common abnormal hemoglobins is hemoglobin S, which causes sickle cell anemia. When the gene for hemoglobin S is inherited from both parents, all of the hemoglobin in the circulation is hemoglobin S and the individual suffers from severe anemia.
The primary level of chromosome structure in eukaryotes occurs when the DNA molecule is wrapped around histone proteins into particles called nucleosomes. Evidence for this “beads on a string” model is derived from nuclease digestion studies. When nuclei are incubated with micrococcal nuclease, the enzyme cleaves the linker DNA between nucleosomes (the string) but not the nucleosomal core DNA (the beads).
The emission of light by living organisms is a fascinating process. The genetic system required for luminescence in the bacterium Photobacterium (Vibiro) fischeri is the lux operon. This operon contains a gene for luciferase (the enzyme that catalyzes the light-emitting reaction) and genes for enzymes which produce the luciferins (which are the substrates for the light-emitting reaction.). In this exercise, students create a luminescent population of bacteria by introducing into E.coli a plasmid that contains this lux operon.