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CAIE A-Level Biology 17.2 Selection Question Bank

Practise selection questions by tracing selection pressures, allele-frequency changes, Hardy-Weinberg calculations and selective-breeding decisions in populations.

Syllabus
2028–2030
Course
Biology 9700
Level
A2

Exam points

  • trace selection pressure to differential survival, reproduction and allele-frequency change
  • interpret drift, founder effects or Hardy-Weinberg calculations from population data
  • outline selective breeding using selection, inbreeding, hybridisation and uniform F1 crops

Covered syllabus points

17.2.1—Natural selection mechanism17.2.2—Stabilising, disruptive and directional selection17.2.3—Effects on allele frequencies17.2.4—Antibiotic resistance and selection17.2.5—Hardy-Weinberg principle17.2.6—Selective breeding principles17.2.7—Selective breeding examples

17.2 Natural and Artificial Selection question 1

[Maximum number: 3]

There are more than 600 plant species in the genus Ipomoea. Many species are grown for their attractive flowers, and some species are used as crop plants.

Fig. 3.1 shows Ipomoea purpurea, the common morning glory.

Fig. 3.1

Fig. 3.1

The gene that determines flower colour in I. purpurea has two alleles:
- a dominant allele that results in purple flowers
- a recessive allele that results in red flowers.

A student recorded the flower colour of all the I. purpurea plants in a field.
The student recorded 660 plants with purple flowers and 440 plants with red flowers.
Assuming the Hardy-Weinberg principle applies to this population, calculate the number of plants in the field that are heterozygous.

Use the equations:
p+q=1
p2+2pq+q2=1p^{2}+2 p q+q^{2}=1
Show your working and give your answer to the nearest whole number.

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