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4. Explain the following terms "epistasis" and "dominance". (10%)
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5. The pedigree below shows the inheritance of ataxia, a rare neurological disorder
characterized by uncoordinated movements. Is ataxia caused by a dominant or a recessive
allele? Explain. (10%)
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6. Genes a and b are 20 cM apart. An a+ b +/a+ b+ individual was mated with an a bla b
individual. (a) Diagram the cross and show the gametes produced by each parent and the
genotype of the Fl. (b) What gametes can the FI produce, and in what proportions? (c) If
the FI was crossed to a bla b individual, what offspring would be expected, and in what
proportions? (d) Is this an example ofthe coupling or repulsion linkage phase? (e) Ifthe F I
were intercrossed, what offspring would be expected and in what proportions? (15%)
7. Arrange the following events in chronological order, beginning with the earliest: (a)
splicing of an RNA molecule, (b) migration of an mRNA molecule into the cytoplasm, (c)
transcription of a gene, (d) degradation of an mRNA molecule, (e) polypeptide synthesis.
(5%)
8. If a single short-legged sheep should occur in a 'flock, suggest experiments to determine
whether the short legs are the result of a mutation or an environmental effect. If due toa
mutation, how can one determine whether the mutation is dominant or recessive? (10%)
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