O Level Biology 5090 · Topic 17

Inheritance: past paper questions

136 real questionsasked in 8 of the last 10 exam series2019–2025usually: State, Explain, Complete, Describe, Name

Real questions on inheritance

The newest 20 of 47 written questions, plus 89 multiple-choice. Open one to see it on the real paper.

5090/21 · October/November 2025 · Q2b(ii)[2]
One type of cornea plana is caused by a recessive allele. Two people who do not have cornea plana have a child who has the condition. Explain how this is possible.
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5090/21 · May/June 2024 · Q4b(i)[2]
Explain what is meant by the term species.
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5090/21 · May/June 2024 · Q4b(ii)[2]
State the name of the scientific system used to name the species and suggest one advantage of using the scientific name rather than the common name. name of system advantage
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5090/22 · May/June 2024 · Q2b(i)[2]
Define the term species.
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5090/22 · May/June 2024 · Q2b(ii)[1]
State the species name of the organism shown in Fig. 2.1.
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5090/22 · May/June 2024 · Q3a[5]
Complete Table 3.1, using terms from the list below to match each description to a term. phenotype heterozygous dominant homozygous gene genotype allele recessive Table 3.1 description term a form of a gene that codes for one of a pair of contrasting features a form of a gene that always has an effect when it is presen...
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5090/22 · May/June 2024 · Q3b(i)[1]
State the term which describes the shape of the DNA molecule.
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5090/22 · May/June 2024 · Q3b(iv)[2]
Outline the importance of the sequence of A, T, G and C in DNA.
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5090/21 · October/November 2023 · Q4b(i)[2]
Give the name of this type of variation in a population and explain your answer. type of variation explanation
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5090/21 · October/November 2023 · Q4b(ii)[2]
Describe what is meant by the term dominant allele.
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5090/21 · October/November 2023 · Q6a(i)[1]
Name this molecule.
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5090/21 · October/November 2023 · Q6a(ii)[3]
Describe three features of the structure of this molecule.
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5090/21 · October/November 2023 · Q6b[2]
Animal and bacterial cells contain this molecule. Describe how the location and shape of the molecule differ in animal and bacterial cells. location shape
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5090/21 · October/November 2023 · Q6c[3]
Explain how this molecule controls cell function.
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5090/22 · October/November 2023 · Q4c[5]
The dramatic shape and colour of Siamese fighting fish are produced by selective breeding. Suggest how the process of selective breeding in Siamese fighting fish can be used to produce these desirable features.
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5090/21 · May/June 2023 · Q5c[3]
Iris colour is genetically determined. The allele for blue colour, b, is recessive to the allele for brown colour, B. Explain why it is not possible to have a heterozygous blue-eyed person.
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5090/21 · May/June 2023 · Q6c[5]
Describe how the process of natural selection has led to the development of strains of antibiotic-resistant bacteria.
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5090/22 · May/June 2023 · Q7a[5]
The paragraph below describes the structure of a DNA molecule. Complete the paragraph by writing the most appropriate word or letter in each space. DNA contains the chemical elements carbon, hydrogen, oxygen, and . Two strands of DNA coil together to form a double . Each strand is made up of a chain of . Bonds between...
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5090/21 · October/November 2022 · Q2b(i)[1]
State the meaning of the term mutation.
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5090/21 · October/November 2022 · Q3a(i)[1]
Explain the difference between a gene and an allele.
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What examiners said

Less than a quarter of candidates correctly identified ‘discontinuous’ as the type of variation and only a very few of those could correctly explain their answer.
— Examiner report, October/November 2023, 5090/21 Q4(b)(i) (Cambridge)

Describing what is meant by ‘dominant allele’ proved very challenging. Many candidates simply said that it was the strongest, or the allele with the capital letters. There were a small number of excellent answers including statements such as ‘alternative form of a gene’ and ‘expresses itself in the heterozygous state’.
— Examiner report, October/November 2023, 5090/21 Q4(b)(ii) (Cambridge)

Many candidates appreciated that DNA formed a double helix and there were also many correct references to two strands and the base pairing of C to G and A to T.
— Examiner report, October/November 2023, 5090/21 Q6(a)(ii) (Cambridge)

Practise this topic

Answer these questions online and get each one marked against the official mark scheme, with what you missed and how to fix it.

Practise inheritance

In the syllabus

17.1 Variation

Describe variation as differences between individuals of the same species
Understand that continuous variation results in a range of phenotypes between two extremes, including body length and body mass
Understand that discontinuous variation results in a limited number of phenotypes with no intermediates, including ABO blood groups, seed shape and seed colour in peas
Understand that discontinuous variation is usually caused by genes only and continuous variation is caused by genes and the environment
Investigate and describe examples of continuous and discontinuous variation

17.2 DNA

Describe the structure of a DNA molecule: (a) two strands coiled together to form a double helix (b) each strand is made up of a chain of nucleotides (c) each nucleotide contains a base (A, T, C, G; full names are not required) (d) bonds between pairs of bases hold the strands together (e) the bases always pair up in the same way: A with T, and C with G
Define a gene as a length of DNA that codes for a protein
Explain that DNA controls cell function by controlling the production of proteins, including enzymes
State that the sequence of bases in a gene determines the sequence of amino acids needed to make a specific protein (knowledge of the details of nucleotide structure is not required)
Understand that different sequences of amino acids give different shapes to protein molecules

17.3 Inheritance

Describe inheritance as the transmission of genetic information from generation to generation
Define an allele as an alternative form of a gene
Understand and use the terms: dominant, recessive, phenotype, genotype, homozygous and heterozygous
Use genetic diagrams, including Punnett squares, to predict the results of monohybrid crosses and calculate phenotypic ratios, limited to 1 : 1 and 3 : 1 ratios
Explain why observed ratios often differ from expected ratios, especially when there are small numbers of offspring
State that two identical homozygous individuals that breed together will be pure-breeding
Explain codominance by reference to the inheritance of the ABO blood groups (phenotypes A, B, AB, O, gene alleles IA, IB and Io)
Describe the determination of sex in humans (XX and XY chromosomes)
Describe a gene mutation as a random change in the base sequence of DNA, using sickle cell anaemia as an example
Describe a chromosome mutation as a change in the chromosome number or structure, using Down’s syndrome as an example (47 chromosomes instead of 46)
State that mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations
Understand that ionising radiation and some chemicals increase the rate of mutation

17.4 Selection

Describe natural selection with reference to: (a) variation within populations (b) production of many offspring (c) struggle for survival, including competition for resources (d) reproduction by individuals that are better adapted to the environment than others (e) passing on of their alleles to the next generation
Describe how the inherited features of a population can evolve over time as a result of natural selection
Describe the development of strains of antibiotic-resistant bacteria, including MRSA, as an example of natural selection
Describe artificial selection (selective breeding) with reference to: (a) selection by humans of animals or plants with desirable features (b) crossing these to produce the next generation (c) selection of offspring showing the desirable features (d) repetition over many generations
Describe the role of artificial selection in the production of economically important plants and animals

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