Genetics – Problem Solving

 

 

 

You are interested in how organisms metabolize alcohol. You learn that fruit flies respond to alcohol and decide to take a genetic approach to identify the associated genes. Normally, treatment of flies with vapor containing 1% alcohol for 30 minutes results in 50% of the flies passing out due to intoxication. You identify mutations in four genes that affect this behavior:

sloshed: all flies pass out after 30 minutes

lightweight: all flies pass out after 30 minutes

boozer: 25% of flies pass out after 30 minutes

drunk: 25% of flies pass out after 30 minutes

a. Assuming that all of these are recessive loss-of-function mutations, what double mutants would you construct to determine if these genes act in the same genetic pathway or not? Please indicate why you make the choices you do and predict the results that would indicate the genes function in a single pathway. What results would indicate the genes do not act in the same pathway?

b. Assuming that you find evidence for a single genetic pathway, what double mutants would you construct to determine the order of gene function? Again, indicate why you make the choices you do.

c. boozer; slosheddouble mutant flies all pass out after 30 minutes, whereas 25% ofboozer; lightweightdouble mutant flies pass out after 30 minutes. Can you draw a pathway? What is it? What phenotype is the boozer; sloshed; lightweighttriple mutant expected to have? Please describe your scientific reasoning.

After more thorough genetic screening, you discover a rare, dominant gain-of-functionmutation, pansy, where no flies pass out after 30 minutes of treatment with 1% alcohol vapor. For double mutants of pansy(gain-of-function)with sloshed, all flies pass out after 30 minutes with 1% alcohol.You look for null mutations in pansythat might assist with pathway analysis, but fail to find any (the screening is easy, as one simply treats mutagenized flies with 1% alcohol and looks to see who survives at 30 minutes). Eventually, via more mutant screens, you identify a recessive null allele of pansythat is embryonic lethal and displays massive abnormalities in neural development. Double mutants ofpansy(loss-of-function)with sloshedare viable and all flies pass out when treated with 1% alcohol for 30 minutes, whereas double mutants ofpansy(loss-of-function)with lightweight are embryonic lethal.

d. Where (if anyplace) does pansyacts in the alcohol susceptibility pathway?

e. Please discuss the relationship of pansyand sloshedat the molecular level with regards to neuronal development/function.

f. You clone boozerand drunk. Overexpression of either of these genes results in all flies passing out after treatment with 1% alcohol for 30 minutes. Overexpression of boozerin a drunk null background results in all flies passing out after 30 minutes with 1% alcohol. Overexpression of drunkin a boozernull background results in no flies passing out after 30 minutes with 1% alcohol. Overexpression of either drunkor boozerin a pansy(gain-of-function)background results no flies passing out after 30 minutes with 1% alcohol.

 

 

 

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