Species and courtship behaviourAQA A-Level Biology: Subtopic test

1. 1
   A horse has 64 chromosomes in each body cell and a donkey has 62. A horse and a donkey can mate and produce a healthy offspring called a mule. A mule has 63 chromosomes in each body cell. Mules have never been reported to produce offspring of their own.

   (a)

   Which statement correctly explains why the horse and the donkey are classed as different species?

   [1 mark]

   • AThey can mate, but the offspring produced is not fertile
   • BThey have different numbers of chromosomes, so cannot mate
   • CThey live in different habitats
   • DThey produce offspring that are all identical to each other

   (b)

   Which is the most likely reason why a mule is infertile?

   [1 mark]

   • AMules do not have any sex organs
   • BMules lack courtship behaviour
   • CChromosomes cannot be separated evenly in meiosis, as the 63 chromosomes do not form homologous pairs
   • DMules have more chromosomes than their parents

   (c)

   Explain why the horse and the donkey are classified as separate species even though they can mate.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two closely related species of fruit fly live in the same forest. In species P, the male produces a courtship song by vibrating one wing, with pulses 40 milliseconds apart. In species Q, the male's song has pulses 70 milliseconds apart. In a laboratory test, females of species P accepted a male for mating after hearing a song with 40 millisecond pulses, but almost never after hearing a song with 70 millisecond pulses.

   (a)

   What is the main role of the song in the courtship of the fruit flies?

   [1 mark]

   • AIt frightens other males away
   • BIt allows the female to recognise a male of her own species
   • CIt makes the male's wings stronger
   • DIt makes the female more able to produce eggs

   (b)

   A female of species P mates with a male of species Q. Which outcome is the most likely?

   [1 mark]

   • AWasted gametes and energy, because no fertile offspring would be produced
   • BFertile offspring with a higher survival rate
   • CFertile offspring with a different chromosome number
   • DA stronger courtship song in the next generation

   (c)

   Explain why courtship behaviour is a necessary precursor to successful mating.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Two species of firefly live in the same meadow. The males of each species fly at night and give a pattern of flashes that is different in each species. A female on the ground replies with a single flash after a fixed delay. A researcher imitates the flash pattern of species X with a torch. Females of species X replied on 85% of the occasions, but females of species Y, a related species, replied on only 6% of the occasions.

   (a)

   Explain the role of the flash patterns in species recognition in the fireflies.

   [3 marks]

   (b)

   Use the data and the definition of a species to explain why the courtship flash pattern is important to species X.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Two closely related species of frog breed in the same pond in spring. Males of each species give a call that is different in each species, and then perform a set courtship sequence before the female releases her eggs. In captivity the two species can be made to mate, and the offspring grow into healthy adults, but these adults never produce young.

   (a)

   Explain how courtship behaviour increases the chance of successful reproduction in these frogs.

   [6 marks]

   (b)

   The two frog species can be made to mate and produce healthy adults. Evaluate whether they should be classified as the same species or as different species.

   [6 marks]

   Total for question 4: 12 marks

End of questions