Genetic diversity, adaptation and taxonomyAQA A-Level Biology: Topic test

1. 1
   Warfarin is a poison used to control rats. In a population of brown rats, a few rats carried an allele that gave resistance to warfarin. After warfarin had been used for many years, most of the rats in the population carried the allele.

   (a)

   Which term describes the number of different alleles of this gene in the rat population?

   [1 mark]

   • AGenetic diversity
   • BSpecies richness
   • CAn adaptation
   • DSpecies recognition

   (b)

   Which type of selection is shown by the change in the rat population?

   [1 mark]

   • AStabilising selection
   • BRandom mutation
   • CSpecies recognition
   • DDirectional selection

   (c)

   Explain how the resistance allele became common in the rat population after warfarin was introduced.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Males of two species of jumping spider, P and Q, perform a courtship display of leg waving. The pattern of waving is different in each species, and a female accepts a male only if his pattern matches that of her own species. In a laboratory, a P male and a Q female were forced together and mated. The offspring grew into adults but produced no gametes.

   (a)

   What is the main role of the courtship display?

   [1 mark]

   • AIt increases the number of eggs a female produces
   • BIt allows females to recognise males of their own species
   • CIt causes mutations that make offspring different
   • DIt makes males of the two species genetically identical

   (b)

   What do the results of the forced mating show?

   [1 mark]

   • AP and Q are the same species because they produced offspring
   • BP and Q are the same species because they have similar courtship
   • CP and Q are different species because their offspring are infertile
   • DP and Q are different species because the female was forced to mate

   (c)

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

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The English oak (Quercus robur) and the sessile oak (Quercus petraea) are both in the genus Quercus. The beech (Fagus sylvatica) is in the genus Fagus. All three species belong to the same family, Fagaceae. A 600-base section of one gene was sequenced in each species. The two oaks differ at 3 bases. The English oak and the beech differ at 36 bases.

   (a)

   Explain what is meant by a binomial, using the English oak as an example, and state the smallest taxon from those given that includes both oaks but not the beech.

   [3 marks]

   (b)

   Calculate the percentage difference in the base sequence for each comparison, and explain how the results support the classification of these three species.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Aphids are small insects that feed on crop plants. In a field of potato plants that was sprayed regularly with an insecticide, the percentage of aphids carrying an allele for resistance to the insecticide rose from 2% to 85% over eight years. Aphids from a neighbouring field of beet plants look identical, but males from one field do not respond to the courtship pheromone released by females from the other field. A researcher wants to find out whether the aphids from the two fields are different species.

   (a)

   Explain how the percentage of aphids carrying the resistance allele in the potato field rose from 2% to 85%.

   [6 marks]

   (b)

   Describe how the researcher could decide whether the aphids from the two fields are different species, and explain the importance of the pheromone observation and of DNA sequence data in reaching a decision.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Three species in the family Canidae are the grey wolf (Canis lupus), the coyote (Canis latrans) and the red fox (Vulpes vulpes). The classification is phylogenetic.

   (a)

   Which is the smallest taxon from this list that includes all three species?

   [1 mark]

   • AGenus
   • BSpecies
   • CFamily
   • DOrder

   (b)

   According to this classification, which two species are the most closely related?

   [1 mark]

   • AGrey wolf and red fox
   • BGrey wolf and coyote
   • CCoyote and red fox
   • DAll three are equally related

   (c)

   Explain why the red fox is placed in a different genus from the grey wolf and coyote.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   In a small bird species, pairs lay between 2 and 8 eggs. Pairs that lay 4 or 5 eggs rear the most chicks to adulthood. Pairs that lay 2 eggs rear few chicks, and pairs that lay 8 eggs cannot feed all their chicks, so many chicks starve. Clutch size is partly controlled by genes.

   (a)

   Which type of selection acts on clutch size in this bird?

   [1 mark]

   • ADirectional selection
   • BCourtship selection
   • CAn adaptation
   • DStabilising selection

   (b)

   What change in clutch size is expected over many generations?

   [1 mark]

   • AMost pairs lay 4 or 5 eggs, with fewer pairs laying very small or very large clutches
   • BThe mean clutch size increases steadily to 8
   • CThe mean clutch size decreases steadily to 2
   • DAll pairs lay exactly 3 eggs

   (c)

   Distinguish between directional selection and stabilising selection.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Two populations of a plant-hopper insect, X and Y, live on different grass species. In 100 laboratory pairings of an X male with a Y female, only 12 pairs mated and produced offspring, and all 60 of those offspring were infertile. Within population X, 94 of 100 pairings produced offspring, all of them fertile. X males perform a courtship display of rhythmic body vibrations, and Y females usually did not respond to it.

   (a)

   Calculate the percentage of X male and Y female pairings that produced offspring, and use all of the information to decide whether X and Y belong to the same species.

   [3 marks]

   (b)

   Explain how courtship behaviour helps to account for the low number of successful pairings between X males and Y females.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Antibodies against human serum albumin were mixed with serum albumin from four other primates. The stronger the reaction, the more similar the albumin is to human albumin. The reaction as a percentage of the reaction with human albumin was: chimpanzee 98, gorilla 95, orangutan 88, gibbon 81. Genome sequencing showed the same order of similarity in the base sequences of the albumin genes. Gibbons have long arms for swinging through trees, and each mated pair sings a courtship duet that is specific to the gibbon species.

   (a)

   Explain how these data can be used to suggest the evolutionary relationships between humans and the four primates, and how this information is used in a phylogenetic classification.

   [6 marks]

   (b)

   Explain how long arms could have evolved in gibbons by natural selection, and explain the importance of the courtship duet for successful mating.

   [6 marks]

   Total for question 8: 12 marks

End of questions