1. 1
   A student is researching a genetic condition in which a single gene, found on a particular chromosome, codes for a protein called haemoglobin. A mutation in this gene results in the production of a differently shaped haemoglobin protein, which affects the way red blood cells carry oxygen.

   (a)

   Which statement below best defines a gene?

   [1 mark]

   • AA length of DNA that codes for a protein
   • BA structure made of two DNA strands coiled together that stores an organism's entire genetic information
   • CAn alternative form of a characteristic, controlled by two or more genes
   • DA molecule that carries amino acids to the site where a chromosome is assembled

   (b)

   Which molecule carries a copy of the gene's base sequence from the nucleus to the ribosomes in the cytoplasm, where it is used to assemble the protein?

   [1 mark]

   • ATransfer RNA (tRNA)
   • BMessenger RNA (mRNA)
   • CDNA ligase
   • DA restriction enzyme

   (c)

   Explain how a mutation in the gene for haemoglobin could result in red blood cells that carry oxygen less effectively, in terms of the protein that is produced.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An adult human's bone marrow constantly produces new red blood cells to replace old, worn-out cells that are broken down in the liver and spleen. Each new red blood cell is produced by a type of nuclear division that produces genetically identical daughter cells.

   (a)

   What is the name of the type of nuclear division that produces the new, genetically identical red blood cells described above?

   [1 mark]

   • AMeiosis
   • BFertilisation
   • CMitosis
   • DMutation

   (b)

   Before this type of nuclear division takes place, what must happen to the chromosomes in the parent cell?

   [1 mark]

   • AThey must pair up with a chromosome from a different cell
   • BThey must be halved in number
   • CThey must be broken down into individual genes
   • DThey must be exactly replicated, producing two identical copies of each chromosome

   (c)

   State two roles that mitosis plays in the human body, other than the production of new red blood cells described above.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Domestic dogs have 78 chromosomes in each body (diploid) cell, arranged as 39 pairs. When a male dog produces sperm cells and a female dog produces egg cells, a type of nuclear division called meiosis occurs in the testes and ovaries respectively to form these gametes.

   (a)

   State the number of chromosomes present in one dog sperm cell, and explain why this number is different from the number of chromosomes in a dog body cell.

   [3 marks]

   (b)

   Explain how meiosis, unlike mitosis, results in genetically different gametes being produced, and explain why this genetic difference between gametes is important for a population of dogs.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In fruit flies, red eye colour (allele R) is dominant over white eye colour (allele r). A fly breeder crosses a red-eyed fly that is heterozygous for this gene with a white-eyed fly, and wants to predict the possible eye colours and ratio of offspring produced.

   (a)

   Determine the genotypes of the two parent flies described above, and predict the possible genotypes, phenotypes and phenotypic ratio of their offspring, showing your reasoning.

   [6 marks]

   (b)

   Explain how the alleles R and r came to be present at the same position on a pair of chromosomes in the heterozygous red-eyed parent fly, and explain how meiosis ensures that each gamete produced by this parent receives only one of the two alleles.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A brewery is studying a gene in a strain of yeast that codes for an enzyme called invertase, which is needed to break down sucrose into simpler sugars during fermentation. A mutant strain of yeast carries a different version of this gene, which the brewery wants to investigate the effect of.

   (a)

   What term is used to describe two different forms of the same gene, such as the normal and mutant versions of the invertase gene described above?

   [1 mark]

   • AAlleles
   • BChromosomes
   • CSpecies
   • DGenomes

   (b)

   The mutant version of the gene arose as a result of a random change in the sequence of bases in the yeast's DNA. What term describes this kind of change?

   [1 mark]

   • AFertilisation
   • BMeiosis
   • CMutation
   • DSelection

   (c)

   Explain how a change in the sequence of bases in the mutant gene could result in the yeast producing a non-functional form of the invertase enzyme.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Some species of lizard can regrow a lost tail after it has been shed to escape a predator. The new tail tissue is formed by cells at the site of the wound repeatedly dividing to produce large numbers of new cells, which then become part of the regenerated tail.

   (a)

   What type of nuclear division produces the large numbers of new, genetically identical cells that form the regenerated tail?

   [1 mark]

   • AMeiosis
   • BMitosis
   • COsmosis
   • DDiffusion

   (b)

   Which of the following statements about the daughter cells produced by this type of nuclear division is correct?

   [1 mark]

   • AThey contain half the chromosome number of the parent cell
   • BThey are genetically different from the parent cell and from each other
   • CThey contain no chromosomes at all
   • DThey are genetically identical to the parent cell and to each other

   (c)

   Before the cells at the wound site can divide by mitosis to regrow the tail, state what must first happen to the chromosomes in each cell, and explain why this is necessary.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Cultivated tomato plants have 24 chromosomes in each body (diploid) cell, arranged as 12 pairs. Meiosis occurs in the anthers of a tomato flower to produce pollen grains, and in the ovary to produce egg cells within the ovules.

   (a)

   State the number of chromosomes present in one tomato pollen grain nucleus, and explain, in terms of chromosome number, why fertilisation between a pollen nucleus and an egg cell nucleus must occur to produce a new tomato plant.

   [3 marks]

   (b)

   Explain the difference between mitosis and meiosis in terms of the number and genetic content of the cells produced, and explain why meiosis, rather than mitosis, must be used to produce the pollen grains and egg cells of the tomato plant.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   In budgerigars, green feather colour (allele G) is dominant over blue feather colour (allele g). A breeder has a green-feathered budgerigar of unknown genotype and wants to determine whether it is homozygous (GG) or heterozygous (Gg) without carrying out DNA testing.

   (a)

   Describe how the breeder could use a test cross to determine the unknown genotype of the green-feathered budgerigar, including the genetic cross(es) needed and how the results would be interpreted.

   [6 marks]

   (b)

   Explain where in the parent budgerigars' bodies the alleles G and g are located, how these alleles are passed on to the offspring, and explain why every body cell of an offspring budgerigar produced from this cross contains the same allele combination for feather colour, even though the offspring is made up of billions of cells.

   [6 marks]

   Total for question 8: 12 marks

End of questions