1. Answer the questions for the two different genes listed below: A. For gene A, in a diploid organism, four units of the protein product are needed for normal function. Each wildtype allele produces five units. If a mutation causes a null allele (no protein product is produced), is this allele dominant or recessive? Explain your reasoning. A. For gene B, in a diploid organism, eight units of the product are needed for normal function. Each wildtype allele produces five units. If a mutation causes a null allele (no protein product is produced), is this allele dominant or recessive? Explain your reasoning. 2. The human piebald trait is a defect in melanocyte development characterized by patches of skin and hair lacking pigmentation. The piebald gene is located on human chromosome four. The condition results from the inability of pigment-producing cells to migrate properly during development. Two parents with piebald spotting have two children. One child has piebald spotting, and the other child has normal pigmentation. A. Is the piebald spotting trait dominant or recessive? Explain why you came to this conclusion. B. What are the genotypes of the parents? 3. C57BL/6, often referred to as "C57 black 6", is a common inbred strain of laboratory mouse. It is the most widely used "genetic background" for genetically modified mice for use as models of human disease. You have been hired as a lab assistant in a mouse research lab. Black coat color is determined by an autosomal dominant gene and the recessive allele of this gene produces mice with white coats. Before an experiment is started you are asked to determine if the black mouse #24 to be used in this experiment is pure-breeding or heterozygous for the black coat trait. The laboratory has purebreeding black mice and pure-breeding white mice that you can use to answer this question. A. What cross would you do to determine the genotype of the mouse #24? B. What results would you expect if mouse #24 was pure-breeding for coat color? C. What results would you expect if mouse #24 was heterozygous for coat color? 4. For a particular plant, tall stems (T) are dominant over short stems (t). A monohybrid cross was made between a pure-breeding tall plant with a pure-breeding short plant. All the F1 progeny were tall plants. The F1 plants were self-crossed to generate F2 plants. Pollen from all the F2 plants was pooled and used to fertilize pure-breeding short stem plants. The resulting 320 plants were analyzed, what proportion of the progeny resulting from this cross would be expected to have short stems? (Show your work and use the gene symbols defined above).