Problem set 61. You find a mouse with no tail. In order to determine whether thismouse carries a new mutation, you cross it to a normal mouse. Allthe F1 progeny of this cross are wild type. What does this mean?You then mate all the F1 males to their sisters and observe that threeout of 42 F2 animals have no tail and two have short tails. Whatcould explain this pattern of inheritance?You map the no tail mutation by recombination and realize that thereis a stock available that is heterozygous for a deletion that removesthe region where the no tail mutation maps. You cross animalswithout tails to animals that are heterozygous for the deletion. Allthe progeny for this cross are wild type. Assuming that the deletionreally removes the gene mutated by your mutation, explain thisresult.2. You are studying the regulation of the lac operon in E. coli andperform a merodiploid (partial diploids) analysis with variousregulatory and structural gene variants that you isolated. Your firstresults are shown below (in units of ß-galactosidase activity). ß-galactosidase activityExperiment Genotype + Inducer - Inducer1. lacI+O+Z+ 100 0.12. lacI-OcZ+ 100 1003. lacI-OcZ- 1 0.14. lacI-O+Z+/lacI+O+Z+ 200 0.1lacI encodes the lac repressor and is active in the absence of inducer(i.e., lac repressor binds to the lac operator and inhibits transcriptionfrom the lac promoter). Addition of inducer inhibits the repressorand stimulates transcription from the lac promoter. lacO is theoperator, the region to which lac repressor binds, and lacOcmutations are constitutive operator mutations, causing lacZexpression in the presence of repressor and absence of inducer. lacZencodes ß-galactosidase, an enzyme that functions as a tetramer.a) Why is the induced activity in experiment 4 twice that of 1.You generate additional merodiploids and get the surprising resultsshown below.Experiment Genotype Induced Uninduced5. lacI-OcZ-/lacI+O+Z+10 0.16. lacI+OcZ-/lacI-O+Z+10 0.17. lacI-O+Z-/lacI+OcZ+10 1008. lacI+OcZ+/lacI-O+Z-10 100b) Describe a hypothesis to explain the results of experiments 5-8.3. Drosophila homozygous for an allele of the thick veins gene, tkvSz2,are normal-appearing adults except that the veins on the wings aremuch thicker than the wild-type wing veins. Flies hemizygous forthat allele and a deficiency of the gene (tkvSz2/Df) die as embryos.a. What is the nature of the tkvSz2 allele (amorph, hypomorph,haploinsufficient, hypermorph, antimorph, neomorph)?b. Based on the mutant phenotypes, what are the functions of thewild-type thick veins gene?4. You compare the phenotype of animals that are homozygous for amutation (m/m), that are heterozygous for the mutation (m/+), thatare hemizygous for the mutation (m/Df), that contain an extra copyof the wild-type gene (m/m/+), and that are hemizygous for thelocus (Df/+). Which of these animals will exhibit a wild-typephenotype, and of the animals that exhibit a mutant phenotype,which will exhibit the more severe phenotype (order the mutantsbased on strength of phenotype) when the mutation is:a. Hypomorphic (Explain your reasoning for each example.)b. haploinsufficientc. antimorphic5. The C. elegans lin-14 gene controls the timing of development in C.elegans. LIN-14 protein is high early in development and graduallydecreases as development proceeds. lin-14 is defined by bothdominant and recessive mutant alleles. Animals that arehomozygous for recessive alleles develop precociously(developmental events occur much earlier than normal) because LIN-14 protein levels are lowered or eliminated, similar to the levels seenlater in development. Animals that contain dominant alleles areretarded in development (developmental events occur much earlierthan normal) because LIN-14 levels are higher than they should belate in development. You are given three lin-14 mutants.a) Animals that are homozygous for mutation A developsprecociously and development is even more precocious when themutation is placed over a deficiency of the locus. What type of amutation is this?b) Animals that are homozygous for mutation B developsprecociously and development is similar when the mutation is placedover a deficiency of the locus. What type of a mutation is this?c) Animals that are heterozygous for mutation C are retarded.Development is less retarded when the C mutation is placed over adeficiency and more retarded when the animals contain one Cmutant gene and two wild-type genes. What type of a mutation
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