Question 1 . C. elegans is a small diploid roundworm used in genetic experiments. When essential muscle genes like actin and myosin in these worms are homozygous for mutations that disrupt the gene significantly, the worms die before they hatch from their eggs with a distinctive paralyzed phenotype. You are a new PhD student and you discover a new gene that also has this same phenotype when mutated. While you expected that this new gene needed for muscle formation might code for a protein in the cytoplasm like actin or myosin, this gene codes for a protein that is found in the nucleus. What do you think the likely role of your newfound gene is? Choose from one of the 5 choices below . Briefly – 2 or 3 sentences maximum – explain your choice.

A. Actin or myosin

B. A protein that transports other proteins into the mitochondria.

C. A protein that represses expression of one or more essential muscle genes .

D. A protein that activates expression of one or more essential muscle genes.

E. A protein that contributes to production of ATP

Question 2. Splicing is complicated. There is constitutive splicing, and then there is regulated alternative splicing, and these molecular events can occur in the same or different tissues.

a. What is constitutive splicing?

b. What is alternative splicing?

c. Draw a gene with three exons and two introns. In this example assume exons 1,2,3 are expressed in one tissue and exons 1,3 are expressed in another. Draw the alternative splicing, and the resulting RNA from this gene.

d. Draw a model illustrating how steric hindrance can promote alternative splicing with in a gene.

e. An individual is heterozygous, one copy of the gene has a mutation in exon 1 and the other copy of the gen e has a mutation exon 3. Draw their genes, with mutations. What RNA molecules can be expressed from these alleles? Will this heterozygote have a mutant or a wild – type phenotype? Explain. Assume the 1/3 variant and the 1/2/3 variant are required in different tissues

Question 3 . You have identified a 4 exon gene expressed in the nervous system of a diploid animal. Different splice variants are expressed in the nervous tissue at the same time. T he organism under study has a gene, unc – 250 , that controls movement and has three different recessive mutant alleles: allele s a 1 , a2 , and a3 . All three mutations are nonsens e stop mutations. When a diploid organism is homozygous for allele a 1 animals die. When homozygous for either allele a2 , or allele a3 , animals are very uncoordinated in their movement (unc). Alleles a2 and a3 fail to complement allele a1 , that is to say a1 / a2 and a 1 / a3 heteroallelic animals are very uncoordinated in their movement (unc). However, a2 / a3 animals are wild type, ie they complement. Using alternative splicing construct a logical model for these observations and show where each of the mutations would be located in the gene.