Question

To find more genes related to sleep you decide to do a mutagenesis screen in the model organism Drosophila melanogaster. Sleep in flies is defined as behavioral immobility for 5 or more minutes. Wild-type flies sleep between 9-15 hours every day.

In order to study the genetics of sleep, you would like to obtain fly mutants that sleep too little. To obtain these mutants, you could collect flies in the wild and look for those that do not sleep very much. However, a faster way is to treat a laboratory strain of flies with a chemical mutagen called EMS (short for ethyl methane sulfonate).

Important background info on EMS: The most common change induced by EMS is the addition of an ethyl group to guanine (G), allowing it to pair with thymine (T). This mistaken pairing leads to G/C --> A/T mutations in the next round of replication. EMS makes mutations randomly throughout the genome. The typical dose of EMS is set so there is usually only one mutation per gamete and that mutation is on one chromosome of a homologous pair.

1. You treat a wild-type male fly with EMS. What type of cell are you hoping will be targeted by the EMS and why is this important (hint: you are mating the flies in the next generation)?

2. What types of mutations (missense, nonsense, silent, insertion, deletion) do you expect to occur in living male flies after treatment with EMS?

3. You are interested in finding fly mutants that sleep too little. In order to do that, you need to first develop a way to assay how often flies sleep. Design an experiment you could perform on flies to characterize an abnormal sleep phenotype. Make sure to include a control in your experiment.

Answer 1

1. Male gamete is sperm cells, hence mutation in male gamete sperm cell is important to get sleep mutant flies in next generation

2. Missense mutation is expected to occur through tretaments since it is not lethal and missense mutation results in change in aminoacid that might cause changes in protein activity which are important for sleep. Other mutations mentioned above could be lethal

3. Control flies without EMT treatmnent and flies which are treated with EMT will be experimental flies. To get flies which sleeps less, behavioural assesment on wild type and EMT treated flies based on immobility will be calculated. The flies which has significantly less immobility when compared to control wild type flies can be considered as less sleeping flies