Lab+7+Genetics+of+Organisms

In this laboratory you will use fruit flies to examine the results of genetic crosses. You will learn how to collect data from the F 1 and F 2 generations and analyze the results from selected crosses using the chi-square test. At the completion of this laboratory you should be able to: · Conduct a genetics experiment for a number of generations. · Recognize patterns of inheritance for simple dominants, recessives, and sex-linked traits. · Analyze the data from your genetic crosses using the chi-square test. //Drosophila melanogaster//, the fruit fly, is an excellent organism for genetics studies because it has simple food requirements, occupies little space, is hardy, completes its life cycle in about 12 days at room temperature, produces large numbers of offspring, may be immobilized readily for examination and sorting, and has many types of hereditary variations that can be recognized with low-power magnification. //Drosophila// have a small number of chromosomes (2n = 8). These chromosomes are easily located in the large salivary gland cells. //Drosophila// exists in stock cultures that can be readily obtained from several sources. Much research about the genetics of //Drosophila// over the last 50 years has resulted in a wealth of reference literature and a knowledge about hundreds of its genes. __ Life Cycle of //Drosophila// __ //Drosophila// have a life cycle with complete metamorphosis and four distinct stages. The life cycle can be completed in about 10-12 days and is illustrated in Figure 1. 1. The eggs - The eggs are small and ellipsoid and have two filaments at one end. They are usually laid on the surface of the culture medium and, with practice, can be seen with the naked eye. The eggs hatch into larvae after about a day. 2. The larval stage - The wormlike larva eats almost continuously, and its black mouth parts can easily be seen moving back and forth in the culture medium. Larvae channel through the culture medium while eating; thus channels are a good indication of the successful growth of a culture. The larva sheds its skin twice as it increases in size. In the last larvae stage, the cells of the salivary glands contain giant chromosomes, which may be seen readily under low-power magnification after proper staining. 3. The pupal stage - When a mature larva is about to become a pupa, it usually climbs up the sideof the culture vial. The last larval covering then becomes harder and darker, forming the pupa case. Through this case the later stages of metamorphosis to an adult fly can be observed. In particular, the eyes, the wings, and the legs become readily visible. 4. The adult stage - When metamorphosis is complete, the adult flies emerge from the pupa case. The are fragile and light in color and their wings are not fully expanded. These flies darken in a few hours and take on the normal appearance of the adult fly. They live a month or more and then die. A female does not mate for about 10-12 hours after emerging from the pupa. Once she has mated, she stores a considerable quantity of sperm in receptacles and fertilizes her eggs as she lays them. Hence, to insure a controlled mating, it is necessary to use females that have not mated before (virgins). Figure 1.
 * Genetics of Organisms **
 * Overview **
 * Background **

YOU ARE ALL BIG KIDS....YOU CAN DO THE REST WITH THE KNOWLEGDE YOU HAVE FROM DOING THE LAB!!! ~Miss Scott