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.