Lesson 3.7.1.1

3.7.1.1 Alleles, genotypes and phenotypes Quiz: AQA Biology, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.1.1, Alleles, genotypes and phenotypes: 20 multiple choice questions for the AQA Biology (7402), Unit 7: Genetics, populations, evolution and ecosystems, written with Revision Ninja.

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The 20 questions

  1. What is a genotype?

    • The observable expression of genes in an organism
    • The genetic constitution of an organism
    • A form of a gene that codes for a particular enzyme
    • The position of a gene on a chromosome

  2. What is a phenotype?

    • The sequence of bases in a single gene, which determines the amino acid order of the polypeptide that the gene codes for
    • The complete set of genes carried by an organism, including every allele inherited from both parents at every locus on every chromosome
    • The number of alleles present in one gamete, which is always half the total number of alleles carried by the parent organism
    • The expression of the genetic constitution and its interaction with the environment

  3. What is a locus?

    • The sequence of bases in one allele
    • The number of alleles present in one gamete
    • The position of a gene on a chromosome
    • The type of cell in which a gene is expressed

  4. In a codominant pair of alleles, what happens in a heterozygote?

    • Both alleles are fully expressed in the phenotype
    • Only one allele is expressed and masks the other
    • Only the allele from the father is expressed
    • Neither allele is expressed in the phenotype

  5. An organism is homozygous at a locus if it has:

    • Two different alleles at that locus
    • Two identical alleles at that locus
    • Three or more alleles at that locus
    • No alleles at that locus

  6. A diploid organism has:

    • Two alleles at each locus, one from each parent
    • One allele at each locus, from one parent only
    • Four alleles at each locus from two parents
    • Two copies of each chromosome, both from the mother

  7. What is meant by multiple alleles?

    • More than two forms of a gene exist in a population, though each individual carries only two
    • An individual carrying three alleles of one gene, which is common in diploid organisms that have three copies of their chromosomes
    • A gene with exactly two alleles in every population, so that each individual must carry one of the two forms of that gene in every case
    • Alleles located on different chromosomes at the same locus, which means that the two forms of the gene can lie anywhere in the genome

  8. The ABO blood group phenotype AB has which genotype?

    • I^O I^O
    • I^A I^B
    • I^A I^A
    • I^A I^O

  9. A recessive allele for white flowers is r and red is R, with R dominant. Which genotype gives white flowers?

    • Rr and RR together
    • Homozygous dominant RR
    • rr
    • Heterozygous Rr

  10. Humans have how many copies of an autosomal gene in each body cell?

    • 23
    • 4
    • 1
    • 2

  11. Pea seed shape is controlled by R for round and r for wrinkled, with R dominant. Which genotype is a round heterozygote?

    • Homozygous dominant RR
    • Rr
    • rR and rr together
    • Recessive rr

  12. A dominant allele for normal enzyme production is paired with a recessive allele for a faulty enzyme. Why is the heterozygote usually phenotypically normal?

    • The dominant allele stops the recessive allele being transcribed
    • The recessive allele is destroyed before it is expressed
    • One dominant allele makes enough functional enzyme to mask the recessive allele
    • The recessive allele makes a larger amount of enzyme that compensates

  13. Which statement correctly describes a heterozygote at one locus?

    • It carries two different alleles and may express one or both depending on dominance
    • It carries alleles on two different chromosomes that never interact
    • It carries two identical alleles and always expresses both
    • It carries only one allele, so its phenotype is always recessive

  14. An organism with genotype AaBbCc is assumed to show independent assortment. How many different gamete types can it produce?

    • 6
    • 12
    • 3
    • 8

  15. Why does a trait such as human height show a range of values across a population?

    • Phenotype depends on both genotype and environment, so people with similar genotypes may differ in height
    • Height depends only on the age of the individual, since growth stops at a fixed age in every person whatever their diet or genes
    • Each gene in height has three alleles, so there are only three possible heights that a person can reach as an adult in any population
    • Height is controlled by a single gene with no environmental influence, so the heights of people within a family are always identical

  16. Why can the phenotype alone not always identify the genotype?

    • Dominant homozygotes and heterozygotes show the same dominant phenotype
    • Genotypes are visible under a light microscope, so phenotypes are not needed
    • Recessive phenotypes can never be produced by heterozygotes
    • Environmental factors always cancel out genetic differences

  17. In a heterozygote for a dominant trait, which alleles are expressed in the phenotype?

    • Both alleles are masked and neither is expressed
    • The dominant allele is expressed and the recessive allele is masked
    • Both alleles always give an intermediate phenotype
    • The recessive allele is expressed and the dominant is masked

  18. A dominant allele A and recessive allele a are present at a locus. What is the phenotype of genotype aa?

    • Intermediate phenotype between dominant and recessive
    • Codominant phenotype with both expressed
    • Recessive phenotype
    • Dominant phenotype

  19. Which factor is most likely to alter the phenotype of an individual without changing its genotype?

    • A change in diet affecting growth
    • A change in the position of a locus on the chromosome
    • A change in the base sequence of a gene
    • A change in the number of chromosomes in each gamete

  20. Why do two individuals with the same genotype for a trait sometimes show different phenotypes?

    • Environmental factors such as nutrition or climate can influence how the genotype is expressed
    • Genes are not inherited from parents, so every phenotype arises at random and cannot be predicted from the parents' genotypes
    • Their genotypes must differ because their phenotypes differ, so any two individuals who look alike must carry the same alleles
    • Their alleles mutate at different rates during development, so two individuals with identical genotypes at birth may diverge in phenotype

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