Problem set 6 1 You find a mouse with no tail In order to determine whether this mouse carries a new mutation you cross it to a normal mouse All the 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 three out of 42 F2 animals have no tail and two have short tails What could explain this pattern of inheritance You map the no tail mutation by recombination and realize that there is a stock available that is heterozygous for a deletion that removes the region where the no tail mutation maps You cross animals without tails to animals that are heterozygous for the deletion All the progeny for this cross are wild type Assuming that the deletion really removes the gene mutated by your mutation explain this result 2 You are studying the regulation of the lac operon in E coli and perform a merodiploid partial diploids analysis with various regulatory and structural gene variants that you isolated Your first results are shown below in units of galactosidase activity Experiment 1 2 3 4 Genotype lacI O Z lacI OcZ lacI OcZlacI O Z lacI O Z galactosidase activity Inducer Inducer 100 100 1 200 0 1 100 0 1 0 1 lacI encodes the lac repressor and is active in the absence of inducer i e lac repressor binds to the lac operator and inhibits transcription from the lac promoter Addition of inducer inhibits the repressor and stimulates transcription from the lac promoter lacO is the operator the region to which lac repressor binds and lacOc mutations are constitutive operator mutations causing lacZ expression in the presence of repressor and absence of inducer lacZ encodes 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 results shown below Experiment 5 6 7 8 Genotype Induced lacI OcZ lacI O Z lacI OcZ lacI O Z lacI O Z lacI OcZ lacI OcZ lacI O Z 10 10 10 10 Uninduced 0 1 0 1 100 100 b 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 are much thicker than the wild type wing veins Flies hemizygous for that 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 the wild type thick veins gene 4 You compare the phenotype of animals that are homozygous for a mutation m m that are heterozygous for the mutation m that are hemizygous for the mutation m Df that contain an extra copy of the wild type gene m m and that are hemizygous for the locus Df Which of these animals will exhibit a wild type phenotype and of the animals that exhibit a mutant phenotype which will exhibit the more severe phenotype order the mutants based on strength of phenotype when the mutation is a Hypomorphic Explain your reasoning for each example b haploinsufficient c antimorphic 5 The C elegans lin 14 gene controls the timing of development in C elegans LIN 14 protein is high early in development and gradually decreases as development proceeds lin 14 is defined by both dominant and recessive mutant alleles Animals that are homozygous for recessive alleles develop precociously developmental events occur much earlier than normal because LIN14 protein levels are lowered or eliminated similar to the levels seen later in development Animals that contain dominant alleles are retarded in development developmental events occur much earlier than normal because LIN 14 levels are higher than they should be late in development You are given three lin 14 mutants a Animals that are homozygous for mutation A develops precociously and development is even more precocious when the mutation is placed over a deficiency of the locus What type of a mutation is this b Animals that are homozygous for mutation B develops precociously and development is similar when the mutation is placed over 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 a deficiency and more retarded when the animals contain one C mutant gene and two wild type genes What type of a mutation is this
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