DNA replication

Assignment 1

1. A. Briefly explain how the leading and lagging strands of DNA are synthesized during DNA replication. (10 marks)
2. What is the function of each of the following? (2 marks each, 10 marks total)
   • Primase
   • Helicase
   • Nucleases
   • Histones
   • Poly(A) tail
3. What would be the complementary strand of the following portion of DNA: 3’AACCGTAATTCG5’? (2 marks)
4. Using the following mRNA sequence, provide a definition and an example of each of the following mutations: silent, nonsense, missense, and frameshift mutation. (3 marks each, total 12 marks)

AUG GUG CCA UUC AAU AUG UGG

• Summarize how a mature mRNA is made from the primary mRNA transcript. (6 marks)
• Answer the following two questions: (8 marks total)
• Describe the central dogma of molecular biology. (2 marks)
• Give 3 reasons why proteins are not made directly from DNA. (Hint: Consider disadvantages of using DNA directly, and/or advantages of not using DNA directly). (6 marks)
• Compare and contrast the following which are involved in transcription in Eukaryotes: (4 marks each, 12 marks total)
• Promoter proximal elements and promoter
• Enhancers and silencers
• Regulatory transcription factors and co-activators
• How can one gene code for more than one protein? (2 marks)
• Describe the four levels of chromatin structure and explain how chromatin is decondensed to allow transcription. (10 marks)
• Compare and contrast dideoxy DNA sequencing and Southern blotting with respect to procedure and purpose. (8 marks)

Assignment 2.

1. You are studying a cell which, before the S phase of the cell cycle, has 8 chromosomes and 1.2 picograms (1.2 × 10¹² grams) of DNA. Complete the following table with the expected number of chromosomes, chromatids, and homologous pairs, and the amount of DNA in each area or pole of the spindle at each of the stages indicated. (1/2 mark per box, 10 marks total)

• Including examples, compare and contrast the following: (4 marks each; 16 marks total)
  • Genotype and phenotype
  • Codominance and epistasis
  • Crossing-over and independent assortment
  • Non-disjunction and translocation
• A particular type of pond organism usually reproduces asexually. However, in later summer and as winter approaches it tends to reproduce sexually. Explain why this organism would use two different methods of reproduction at different times of the year. (6 marks)
• A female Drosophila (fruit fly) heterozygous for red eyes and grey body was crossed with a male homozygous for scarlet eyes and ebony body. The two genes are linked on the same chromosome. The following offspring were produced. How many map units would separate them? (Show all your work.) (4 marks)

• In a certain breed of domestic fowl, super comb is dominant to single comb but feather colour shows absence of dominance. Black legs and white legs are homozygous, whereas the heterozygote gives red legs. From crosses between birds heterozygous for both genes, what proportion of the offspring would you expect to be: (Define the alleles and show all your work using a Punnett Square.) (12 marks)
  • Super-combed
  • Black-legged
  • Red-legged
  • Super-combed and red-legged
  • Single-combed and white-legged
• A particular X-linked gene is a recessive lethal that causes death and reabsorption of the embryo at an early stage. A heterozygous female married a man expressing the dominant trait. Define the alleles and show your work in answering the following questions: (5 marks)
  • What proportion of their offspring would be expected to be females?

3. What proportion of the offspring would be expected to be carriers of the gene?
4. Look at the following pedigree. Circles represent females; squares represent males. Coloured circles and squares represent affected individuals. Horizontal lines represent matings; vertical lines represent offspring produced from a mating. (15 marks total)

1. What is the mode of inheritance? Referring to the applicable numbered individuals, explain your reasoning. Your choices are autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked. (10 marks)
2. What are the genotypes of the following individuals (be sure to define the alleles): 4, 5, 8, 11? (5 marks)
3. List 4 features of an ideal organism for the study of genetics. (4 marks)
4. Explain the roles of bicoid, the segmentation genes, and homeotic genes in development of an embryo. (10 marks)
5. Answer the following questions about stem cell research: (10 marks total)
6. Differentiate between multipotent, pluripotent, and induced pluripotent stem cells. Include an example of each. (5 marks)
7. Outline the advantages and disadvantages of iPS cells. (5 marks)
8. Write a short paragraph (not more than 200 words) describing the genetic disorder known as maple syrup urine disease (MSUD). In your discussion, include answers to the following questions, using your own words to write a coherent paragraph in complete sentences. Cite your sources following the citation instructions in Jan A. Pechenik’s A Short Guide to Writing about Biology. (8 marks)

a. How is maple syrup urine disease inherited?

b.Why is it called maple syrup urine disease?

• Briefly explain what causes this disease.
• How many births in North America result in infants with MSUD?

BOOK for reference:

Biological Science, Third Canadian Edition, 3rd edition

• Scott Freeman
• Kim Quillin
• Lizabeth Allison
• Michael Black
• Greg Podgorski
• Emily Taylor
• Michael Harrington
• Joan C. Sharp