Recombinant DNA technology is an invaluable tool for molecular geneticists.



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Answer all questions in the spaces provided

  1. Assume that a female with Down syndrome who carries three copies of chromosome 21 could successfully reproduce with a normal 46­chromosome male.
    1. Draw the arrangement of the three chromosome 21s from the female at metaphase I of meiosis I, ignoring all the other chromosomes. (1 mark)
    2. What proportion of the offspring would be expected to have Down syndrome? Justify your answer. (2 marks)
  2. A pure breed of rabbits with normal ears and normal teeth is introduced into a new habitat and successfully reproduces with the local pure breed which are characterized by floppy ears and overgrown teeth. All of the F1 progeny have floppy ears and normal teeth.
    1. Using ‘F’ (dominant) or ‘f’ (recessive) for floppy ears and ‘M’ (dominant) or ‘m’ (recessive) for overgrown teeth, write the genotypes of the parents of this cross and the F1 progeny. (1 mark)


  1. If F1 males and females were crossed, how many F2 progeny with normal ears and overgrown teeth would be expected out of a total of 64? Assume that the two genes are on different chromosomes. Show your working. (3 marks)
  2. The newly introduced rabbits are black with fluffy hair and the local rabbits are albino with normal hair. All F1 rabbits are black with normal hair. Using the symbols ‘B’ (dominant) or ‘b’ (recessive) for fur colour and ‘A’ (dominant) or ‘a’ (recessive) for type hair, write the genotypes for these two genes for the parents and their F1 progeny. (1 mark)
  3. If F1 rabbits were crossed to bbAaMm rabbits, assuming all genes involved are on different chromosomes, what fraction of the offspring would be of the bbAamm genotype? (3 marks)

the space above this line should be sufficient for your answer

  1. Triple heterozygous female mice for the linked recessive traits y, t, and h were crossed to males that phenotypically express y, t, and h. The following phenotypic ratios were obtained in the progeny (+ denoting the dominant trait of each gene):

+ t h             385 y t h               85

y + h               18 + t +         20

+ + +               90 + + h          1 y + +           401

No other phenotypes were observed.

  1. Classify each class according to the type of crossover that originated them. (1 mark)
  2. Which gene is in the middle? (1 mark)


  1. Calculate the genetic distances between the genes. (2 marks)

the space above this line should be sufficient for your answer


  1. The pedigree below shows an individual affected by a disease inherited in an autosomal recessive pattern. Calculate the probability that II.3 will be a boy heterozygous for the mutation that causes this disease. (2 marks)
  • a) Provide a short definition for each of the following terms:
    1. Spliceosome (1 mark)
    2. Charged tRNA (1 mark)


  • Shine­Dalgarno sequence (1 mark)
  1. Put the following events relating to the expression of a typical eukaryotic gene in the correct order:

Translation; Transcription initiation; RNA export from the nucleus; Splicing (1 mark)


  1. A frameshift mutation has ccurred near the end of an exon of a eukaryotic gene. Will it affect the reading frame of the next exon in the mRNA? Explain your answer. (2 marks)
  • a) In translation, which codon(s) are able to pair with a tRNA with the anticodon 5’­IAU­3′, given that I (inosine) can pair with A or U or C? (1 mark)
    1. Which amino acid(s) would be carried by the tRNA with an anti­codon 5’­IAU­3′? A genetic code table is provided on the next page. (1 mark)
    2. Identify which of the following amino acid changes could result from a mutation involving the substitution of one base for a different base. (3 marks)
      1. Leu­to­Gln
      2. Phe­to­Ser
  • Val­to­Cys

the space above this line should be sufficient for your answer

  1. The enz operon codes for two enzymes (ENZ1 and 2) and is regulated by compound X. Mutations in 4 regions of the operon (termed A, B, C and D) have the following effects where a plus sign (+) signifies that the indicated enzyme is synthesized and a minus sign (­) signifies that it is not.
Compound X Absent Compound X Absent Compound X Present Compound X Present
Wild Type + + ­ ­
Mutation in A ­ + ­ ­
Mutation in B + + + +
Mutation in C + ­ ­ ­
Mutation in D ­ ­ ­ ­


  • Is the enz op ron induced r repressed by compound X in the wild type? (1 mark)
  • State which region (A, B, C or D) corresponds to the following components of the enz operon and provide a brief explanation for your answer. (4 marks)
    1. Regulator gene
    2. Promoter
  • Gene encoding Enzyme 1
  1. Gene encoding Enzyme 2
  1. In the absence of sexual reproduction, bacteria have alternative means for transmission of genetic material.
    • What are the four modes of transmission of genetic material in bacteria? (2 marks)


  • How can gen tic material be transferred directly between two living bacteria, and what are the key features of this process? (4 marks)
  • How can horizontal gene transfer be exploited in molecular biology?

(2 marks)

  1. Recombinant DNA technology is an invaluable tool for molecular geneticists.
    • What are the key features of a cloning vector? You may use a diagram. (3 marks)
    • How can a g ne fragment f interest be inserted into a cloning vector? (3 marks)
  2. Prokaryotic and eukaryotic cells are distinguishable by many features, including their genomes. You have been provided with samples of total DNA from prokaryotic and eukaryotic cells. How could you distinguish the two samples experimentally? (3 marks)

the space above this line should be sufficient for your answer


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