Name KEY SID MCB140 Practice Exam 1 Under harsh environmental conditions C elegans can enter an alternate third larval stage known as the dauer stage Animals can live in this stage for months until conditions improve allowing them exit the dauer stage and complete their life cycle Two types of mutants that are defective in dauer development exist Dauer constitutive mutants enter the dauer stage even when environmental conditions are good and dauer defective mutants are unable to enter the dauer stage The conserved insulin regulatory pathway is required for dauer development Loss of function mutations in genes of the insulin pathway cause either dauer constitutive or dauer defective phenotypes a PI3 kinase is a signaling molecule in the insulin pathway and one of the PI3 kinase subunits is encoded by the age 1 gene In a cross between a homozygous age 1 hermaphrodite and a wild type male individual hermaphrodite F1 cross progeny that are heterozygous for the loss of function age 1 mutation generate all normal not dauer F2 self progeny When individual F2 hermaphrodite self progeny are transferred to separate petri plates 3 4 have F3 self progeny that are normal and 1 4 of them have F3 self progeny that are all dauer The growth conditions used will not induce dauer formation in wild type animals Define the genotypes of the F2 progeny of the heterozygous hermaphrodite and whether they will have normal or dauer progeny Also explain why none of them are dauer 1 4 will be and will have normal progeny 1 2 will be age 1 1 and will have normal progeny 1 4 will be age 1 age 1 and will have all dauer progeny They are not dauer because age 1 is a maternal effect gene 1 Name KEY SID b The FOXO transcription factor is encoded by the daf 16 gene Signaling though the insulin receptor which is encoded by the daf 2 gene activates PI3 kinase which eventually leads to the phosphorylation and inhibition of DAF 16 FOXO From what you know about age 1 and the pathway just described what will be the dauer phenotypes constitutive or defective of daf 2 and daf 16 mutants daf 2 mutants will be dauer constitutive daf 16 mutants will be dauer defective c What double mutant phenotypes would be consistent with the molecular pathway for DAF 2 AGE 1 and DAF 16 described above daf 2 daf 16 5 points and age 1 daf 16 5 points double mutants will be dauer defective They can also put down daf 2 age 1 doubles are dauer constitutive but don t give or take away any points for this answer d You are interested in isolating suppressors of a loss of function mutation in the insulin receptor gene daf 2 You want to screen for recessive suppressors that are not maternal effect using the chemical mutagen EMS Describe what you would look for and what generation you would screen Screen the F2 progeny of mutagenized daf 2 mutants for animals that no longer form dauers 2 Name KEY SID e In your screen you identify eight suppressors Five of the suppressor mutations suppress the daf 2 allele that you used but not other loss of function alleles of daf 2 Because interaction suppressors are rare and because you isolated several suppressors of this type in a small screen you decide that the suppressor mutations are not interaction suppressors What type of suppressors do you think that these five mutations represent Do you think that these suppressors will have effects on mutations in other genes Informational suppressors They should suppress some mutations in other genes since they should be gene nonspecific suppressors f The remaining three suppressors named 1 3 can suppress all daf 2 alleles The three suppressors map to the same region of chromosome I Suppressor 1 is recessive and only partially suppresses the daf 2 mutant some of the double mutants still form dauers Suppressors 2 and 3 completely suppress daf 2 when homozygous Suppressor 2 is recessive but suppressor 3 is dominant Animals homozygous for daf 2 and heterozygous for 3 are partially suppressed forming dauers about 20 of the time The daf 2 homozygotes form dauers 100 of the time You suspect that all of these mutations are in the same gene How do you test this for 1 and 2 and what is the outcome if they are in the same gene Use only genetics You do a complementation test by crossing the two mutants They should fail to complement and most of the cross progeny should not be dauer 3 Name KEY SID g Assuming that all three suppressor mutations 1 3 are in the same gene how do you think that they might change the function of the mutated gene You test your hypothesis How do you do this and what are the expected results Use only genetics 1 should reduce gene function Or hypomorph or partial loss of function 2 should eliminate gene function Or amorph or null 3 should antagonize wild type gene function Or antimorph or dominant negative daf 2 is homozygous in all these strains 1 Df will be more severe more suppression or fewer dauers than 1 1 2 Df 2 2 3 3 will be more severe than 3 which is more severe than 3 h Suppressors 1 3 are mapped to a small region that contains 20 genes How might you define which gene of the 20 is mutated No sequencing allowed Use RNA interference with each of the 20 genes to see which would suppress the daf 2 dauer phenotype There are other wasy that we didn t discuss in class for C elegans Also you might state that they will rescue the suppression of daf 2 by putting in the wildtype gene into the sup daf 2 strain You also might isolate transposon induced alleles as a way to mark the gene 4 Name KEY SID 2 In a screen you identify several new recessive mutations that lead to a loss of R7 You are interested in defining where the genes function and carry out a mosaic analysis using white as a cell autonomous marker The results for mosaic ommatidia are shown below for each mutant What can you say about the site of function for each gene Gene defined by mutant 1 functions in R7 Gene defined by mutant 2 functions in R8 Gene defined by mutant 3 functions in R2 Gene defined by mutant 4 functions in either more than one photoreceptor cell or in cells other than R1 8 Gene defined by mutant 5 functions in cells other than R1 8 5 Name KEY SID 3 In the pedigree below label different individuals that have the same mtDNA For example if three individuals have the same mtDNA label them all with an A Individuals with a different mtDNA with a B etc Label all individuals Because of heteroplasmy a maternally inherited trait can skip generations and show up later Is it possible that
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