You are working in a human genetics laboratory that studies causes and treatments for eye cataracts in newborns
This disease is thought to be caused by a deficiency in the enzyme galactokinase, but the human gene that encodes this enzyme has not yet been identified. At a talk by a visiting scientist, you learn about a strain of baker's yeast that contains a mutation called gal1– in its galactokinase gene. Because this gene is needed to metabolize galactose, the mutant strain cannot grow in galactose medium. Knowing that all living things evolved from a common ancestor and that distantly related organisms often have homologous genes that perform similar functions, you wonder whether the human galactokinase gene can function in yeast. Because you have an optimistic temperament, you decide to pursue this line of experimentation. You isolate mRNA gene transcripts from human cells, use reverse transcriptase to make complementary DNA (cDNA) copies of the mRNA molecules, and ligate the cDNAs into circular plasmid DNA molecules that can be stably propagated in yeast cells. You then transform the pool of plasmids into gal1– yeast cells so that each cell receives a single plasmid. What will happen when you spread the plasmid-containing cells on Petri dishes that contain galactose as a carbon source? How can this approach help you find the human gene encoding galactokinase?
On galactose medium, the original gal1– yeast cells cannot grow, nor can cells that received plasmids containing most human cDNA sequences. However, yeast cells that received a plasmid with the human galactokinase gene will probably be able to grow on galactose medium and produce many progeny. This kind of "selection" procedure is very powerful, because even if only 1 in 100,000 cells has the ability to grow under particular conditions, it will be easy to find it. The other 99,999 cells will die in the Petri dish and will therefore be invisible to the investigator. Indeed, scientists have found that the human galactokinase gene can function perfectly well in yeast and thus can "rescue" the defect of the gal1– mutant. It was initially astonishing that genes from humans can function properly in yeast, but this phenomenon has now been observed for many genes.
You might also like to view...
While wastewater is in an activated sludge tank, much of the organic matter is
A) oxidized. B) adsorbed to the floc. C) incorporated into microbial cells. D) oxidized, adsorbed to the floc, and incorporated into microbial cells.
Biologists around the world spend a great deal of time studying the cytoskeleton of cells
Some of the tools they use in their research include chemicals that interfere with the structure of the cytoskeletal elements or with the activities of the motor proteins that associate with the cytoskeleton to facilitate movement. For example, a family of compounds called cytochalasins disrupts the normal assembly and disassembly of microfilaments. Another compound called colchicine binds to tubulin and prevents the assembly of microtubules. The function of dynein is prevented by a compound known as EHNA (erythro-9-[3-2- (hydroxynonyl)] adenine), and blebbistatin inhibits the activity of myosin. Use this information to answer the following questions. Based on this information, where would you predict blebbistatin to have the greatest effect? A. sperm cell motility B. leading edge formation of a migrating fibroblast C. the contraction at the trailing edge of a fibroblast D. Blebbistatin would likely have no effect on any of these examples of cell movement.
Four of the five factors listed below are densityindependent
factors. Select the exception. a. nutrient supply b. temperature drop c. drought d. volcanic eruption e. hard freeze
If four of the original colonists died before they produced offspring, the ratios of genotypes could be quite different in the subsequent generations. This would be an example of
A) diploidy. B) gene flow. C) genetic drift. D) disruptive selection. E) stabilizing selection.