1. 1
   A biology teacher explains that meiosis is a type of nuclear division that occurs in the ovaries and testes, halving the chromosome number to produce gametes that are also genetically different from one another.

   (a)

   A biology teacher explains that a special type of cell division in the ovaries and testes produces gametes with half the number of chromosomes found in a normal body cell. What is this type of division called?

   [1 mark]

   • AMitosis
   • BMeiosis
   • CBinary fission
   • DOsmosis

   (b)

   A human body cell (diploid) contains 46 chromosomes arranged in 23 pairs. How many chromosomes would you expect to find in a gamete produced by meiosis from this cell?

   [1 mark]

   • A46
   • B92
   • C23
   • D0

   (c)

   Describe meiosis as a type of nuclear division, including what happens to the chromosome number and to the genetic content of the resulting cells.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student uses a diagram to trace the chromosome number through the human life cycle: a diploid body cell in the ovary or testis undergoes meiosis to produce haploid gametes, which then fuse at fertilisation to restore the diploid number in the zygote.

   (a)

   During fertilisation, a haploid sperm nucleus fuses with a haploid egg nucleus to form a zygote. What is the chromosome number of the resulting zygote, compared to a normal human body cell?

   [1 mark]

   • AThe zygote is haploid, with half the chromosome number of a body cell
   • BThe zygote has three times the chromosome number of a body cell
   • CThe zygote has no chromosomes at all
   • DThe zygote is diploid, with the same chromosome number as a body cell

   (b)

   Why is it important that meiosis halves the chromosome number before gametes are formed, given that fertilisation later involves the fusion of two gametes?

   [1 mark]

   • ASo that the chromosome number is restored to the normal diploid number at fertilisation, rather than doubling each generation
   • BSo that the offspring will have no chromosomes at all
   • CSo that mitosis is no longer needed in the offspring
   • DSo that the offspring is always genetically identical to one parent

   (c)

   Explain why the chromosome number would double with every generation if gametes were produced by mitosis instead of meiosis.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A biologist studies a family in which two siblings, born to the same parents, show noticeably different characteristics, and investigates how meiosis and fertilisation together explain both the similarities and differences between siblings and their parents.

   (a)

   A biologist observes that two siblings, both produced by the same parents through sexual reproduction, look noticeably different from one another, despite sharing the same parents. Explain how meiosis contributes to genetic variation between siblings.

   [3 marks]

   (b)

   Explain why meiosis and mitosis, involved in the production and development of a zygote, together mean that offspring share some similarities with their parents while also being genetically different from both parents and from their siblings.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A population geneticist compares a sexually reproducing animal species that relies on meiosis to produce gametes with a closely related asexually reproducing species, studying how each responds to environmental change over many generations, and also investigates a rare mutation affecting the process of meiosis itself in one individual.

   (a)

   A population geneticist studies a species of animal that reproduces exclusively by sexual reproduction, relying on meiosis to produce gametes. She compares this species with a closely related species that has evolved to reproduce only asexually. Explain how meiosis contributes to genetic variation within the sexually reproducing species' population, and discuss why this variation could give the sexually reproducing species an advantage in adapting to a changing environment over many generations, compared with the asexually reproducing species.

   [6 marks]

   (b)

   The geneticist discovers a rare individual in the sexually reproducing species whose cells have a fault in meiosis, so that some of the gametes it produces contain the full diploid chromosome number instead of the normal haploid number. Explain what would happen if one of these faulty diploid gametes were involved in fertilisation with a normal haploid gamete, and discuss why this fault could be harmful to the resulting offspring.

   [6 marks]

   Total for question 4: 12 marks

End of questions