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DP IB Biology: HL

Topic Questions

Home / IB / Biology: HL / DP / Topic Questions / 3. Genetics / 3.1 Genes & Chromosomes / Structured Questions: Paper 2


3.1 Genes & Chromosomes

Question 1a

Marks: 3
a)

Part of the gene coding for a specific polypeptide contains the following base sequence:

CATAGTTGGCCA

The following table contains some of the codons on messenger RNA and the amino acids that they code for:

Codons Amino acid coded for by codons
AUU / AUC / AUA Isoleucine (Ile)
UUA / UUG / CUU / CUC / CUA / CUG Leucine (Leu)
GGU / GGC / GGA / GGG Glycine (Gly)
ACU / ACC / ACA / ACG Threonine (Thr)
UCU / UCC / UCA / UCG Serine (Ser)
GUU / GUC / GUA / GUG Valine (Val)
UAA / UAG / UGA STOP

Using the information provided, identify the amino acid sequence for this part of the polypeptide.

[3 marks]

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    Question 1b

    Marks: 3
    b)

    The cells that synthesise this polypeptide was exposed to a mutagen that caused a substitution mutation that changed the DNA base sequence in the following way:

    CATACTTGGCCA

    Using the table from part a), explain the effect this mutation will have on the polypeptide produced.

    [3 marks]

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      Key Concepts
      Mutation
      Translation

      Question 1c

      Marks: 2
      c)

      This polypeptide forms part of the active site of an enzyme that catalyses a metabolic reaction.

      Suggest the effect that the mutation mentioned in part b) would have on the enzyme.

      [2 marks]

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        Question 1d

        Marks: 1
        d)

        Based on the information provided in part a), explain how it could be possible for a mutation to have no effect on the polypeptide.

        [1 mark]

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          Key Concepts
          Mutation

          Question 2a

          Marks: 1
          a)

          Cri du chat syndrome is a rare genetic disorder caused by a chromosomal abnormality that occurs very early in embryonic development. Babies born with cri du chat syndrome suffer from a variety of symptoms and have a characteristic cry which sounds like the meowing of a cat.

          The karyograms below compare the karyotype of a normal child with one that suffers from cri du chat syndrome.

          h-2a-1

          h-2a-2

          Contrast the karyotype of a normal child with that of a child suffering from cri du chat syndrome.

          [1 mark]

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            Question 2b

            Marks: 2
            b)

            Two genes, SEMA5A and CTNND2, are believed to be involved with brain development in a foetus. These genes are missing from children suffering from cri du chat syndrome.

            Suggest two possible symptoms of children with cri du chat syndrome as a result of this.

            [2 marks]

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              Question 2c

              Marks: 2
              c)

              There are some individuals with cri du chat syndrome that do not differ developmentally from their peers in a significant way.

              Based on the information provided in the karyograms at part a), explain this occurrence.

              [2 marks]

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                Question 2d

                Marks: 1
                d)

                Most of the people affected by cri du chat syndrome do not have a family history of the condition.

                Suggest what this means in terms of the heritability of the syndrome.

                [1 mark]

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                  Key Concepts
                  Eukaryotic Chromosomes

                  Question 3a

                  Marks: 2
                  a)

                  The table below shows the genome size and haploid chromosome number of different organisms.

                  Organism Genome size / base pairs Chromosome number / n
                  Polychaos dubium (single celled eukaryote) 6.7 x 1011 > 100
                  Trumpet lily (plant) 9.0 x 1010 12
                  Mouse 3.5 x 109 20
                  Human 3.2 x 109 23
                  Carp (fish) 1.7 x 109 49
                  Chicken 1.2 x 109 39
                  Housefly 9.0 x 108 6
                  Tomato plant 6.6 x 108 12

                  Calculate the percentage difference in the chromosome number found in the zygotes of chickens compared to those of humans.

                  Show your working and give your answer to three significant figures.

                  [2 marks]

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                    Key Concepts
                    Diploid

                    Question 3b

                    Marks: 2
                    b)

                    The diploid number in an organism is always an even number.

                    Using your knowledge on the behaviour of chromosomes during meiosis, explain the importance of the diploid number in an organism.

                    [2 marks]

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                      Question 3c

                      Marks: 3
                      c)

                      Scientists hypothesised that a high chromosome number leads to the development of a more complex organism.

                      Discuss this hypothesis using the data provided in part a).

                      [3 marks]

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                        Question 3d

                        Marks: 1
                        d)

                        Based on your knowledge of chromosomes, suggest a reason why the genome size of a species does not always seem to correlate with the chromosome number.

                        [1 mark]

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                          Question 4a

                          Marks: 2
                          a)

                          Wilson's disease is a condition caused by a mutation of gene ATP7B located on chromosome 13, which codes for an ion transport enzyme. This enzyme is responsible for transporting copper ions (Cu2+) into bile so that it can be removed from the body through the digestive tract. There are several mutations which may lead to Wilson's disease; one of these mutations involves the replacement of the amino acid histidine by glutamine.

                          Describe the type of mutation that could have led to this disease.

                          [2 marks]

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                            Key Concepts
                            Mutation

                            Question 4b

                            Marks: 2
                            b)

                            Based on the information provided in part a), explain the effect this mutation would have on the transport of copper ions.

                            [2 marks]

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                              Question 4c

                              Marks: 1
                              c)

                              In most cases of Wilson's disease, a sufferer must have two copies of the mutated ATP7B allele before the disease is present.

                              Suggest what this may indicate about the dominance of the ATP7B allele.

                              [1 mark]

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                                Question 4d

                                Marks: 2
                                d)

                                People suffering from Wilson's disease have high levels of free copper in their bloodstream which have been shown to cause damage to the cell membranes of red blood cells.

                                Explain the consequences of this to the sufferer.

                                [2 marks]

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                                  Question 5a

                                  Marks: 5

                                  One mark is available for clarity of communication throughout this question.

                                  a)

                                  Compare and contrast the X and Y chromosome.

                                  [5 marks]

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                                    Key Concepts
                                    Sex Determination

                                    Question 5b

                                    Marks: 3
                                    b)

                                    The sex of a foetus is determined by the father.

                                    Explain this statement.

                                    [3 marks]

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                                      Key Concepts
                                      Sex Determination

                                      Question 5c

                                      Marks: 7
                                      c)

                                      Outline how a substitution mutation can alter the amino acid sequence of a polypeptide by using sickle cell anaemia as an example.

                                      [7 marks]

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