Lesson 3.7.1.2

3.7.1.2 Genetic crosses and inheritance patterns Quiz: AQA Biology, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.1.2, Genetic crosses and inheritance patterns: 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 the expected phenotypic ratio in the F2 generation of a monohybrid cross with complete dominance?

    • 9:3:3:1
    • 1:1
    • 1:2:1
    • 3:1

  2. What is the expected phenotypic ratio of a dihybrid cross between two heterozygotes with independent assortment and complete dominance?

    • 1:2:1
    • 3:1
    • 9:7
    • 9:3:3:1

  3. What is a test cross?

    • A cross between an individual of unknown genotype and a homozygous recessive individual
    • A cross between two homozygous dominant individuals, whose offspring always show the recessive phenotype in every generation
    • A cross between two heterozygous individuals, which shows the expected ratio and so confirms the genotype of both parents directly
    • Self-fertilisation of a heterozygous individual, which is the only way to reveal the genotype of an organism in a single generation

  4. Sex-linked genes are:

    • Genes found only on chromosome 21
    • Genes located on the X chromosome
    • Genes located on mitochondrial DNA
    • Genes located only on autosomes

  5. What is the correct formula for the chi-squared statistic?

    • Sum of (O - E) divided by E
    • Sum of (O - E) squared multiplied by E
    • Sum of (O + E) squared divided by E
    • Sum of (O - E) squared divided by E

  6. A chi-squared test compares four phenotypic classes. How many degrees of freedom are used?

    • 4
    • 2
    • 3
    • 5

  7. Epistasis is best described as:

    • Genes on the same chromosome being inherited together
    • One gene masking or modifying the expression of a different gene
    • A gene being switched off by methylation of its promoter
    • Two alleles of the same gene both being fully expressed

  8. What is the probability that a child of two heterozygous parents (Aa x Aa) will be aa?

    • 1/2
    • 1/4
    • 3/4
    • 1/16

  9. In a cross Bb x bb, what is the expected genotypic ratio of the offspring?

    • 3:1 B to b
    • 9:3:3:1
    • 1:2:1 BB to Bb to bb
    • 1:1 Bb to bb

  10. In a dihybrid cross AaBb x AaBb, what is the probability of an aabb offspring?

    • 1/4
    • 1/8
    • 1/16
    • 9/16

  11. In a cross, 70 round and 30 wrinkled seeds are observed from 100 seeds. The expected ratio is 3:1. What is the chi-squared value?

    • 1.33
    • 0.25
    • 5.00
    • 2.67

  12. A chi-squared value of 1.33 with 1 degree of freedom is compared with a critical value of 3.84 at p = 0.05. What is the correct conclusion?

    • There is a significant difference, so the null hypothesis is rejected
    • There is no significant difference, so the null hypothesis is accepted
    • The expected ratio is disproved at p = 0.05
    • The test cannot be concluded because the degrees of freedom are wrong

  13. A woman who is a carrier of colour blindness (X^c X) has children with a normal man (X Y). What is the probability that a son is colour blind?

    • 0
    • 1/2
    • 1
    • 1/4

  14. Two genes lie close together on the same chromosome. Why does a dihybrid test cross give fewer recombinant offspring than expected for independent assortment?

    • The linked alleles tend to be inherited together, so recombination during meiosis is less frequent
    • The linked alleles always segregate in a 9:7 ratio, because two linked genes always produce complementary gene action in the offspring
    • The linked alleles are always lost during meiosis, so the offspring of the test cross never carry either allele of the two genes
    • The genes are on different chromosomes so they cannot be inherited together, which means that independent assortment always applies to them

  15. A dihybrid cross produces a 9:7 phenotypic ratio. Which genetic explanation fits best?

    • Sex-linked inheritance of both genes, which means that both genes lie on the X chromosome and are passed on by the mother only
    • Complementary gene action, where both dominant alleles are needed for one phenotype
    • Codominance of both genes in every heterozygote, so each gene's two alleles are fully expressed and no allele is ever masked
    • Linkage of the two genes on the same chromosome, which causes the two genes always to be inherited together with no recombination

  16. A dihybrid cross of 160 offspring is expected to show the double dominant phenotype with 9:3:3:1 ratio. How many offspring should show this phenotype?

    • 40
    • 10
    • 90
    • 60

  17. A chi-squared value of 8.20 is calculated with 3 degrees of freedom. The critical value at p = 0.05 is 7.82. What is the correct conclusion?

    • The degrees of freedom must be recalculated, so no conclusion is possible
    • The difference is not significant, so the expected ratio is confirmed
    • The expected ratio is proven to be correct
    • The difference is significant, so the expected ratio is rejected at p = 0.05

  18. A colour-blind daughter has a sex-linked recessive condition. What must be true about her father?

    • He must be a carrier but not colour blind
    • He must be normal because the condition is never passed on by fathers
    • He can be either normal or colour blind, with no effect on the daughter
    • He must also be colour blind, since she receives an X chromosome from him

  19. What phenotypic ratio is expected from a cross of two heterozygotes for a codominant gene?

    • 1:1
    • 3:1
    • 9:3:3:1
    • 1:2:1

  20. Why do genes on the same chromosome give a non-Mendelian ratio in a dihybrid test cross?

    • They tend to be inherited together, so recombinant offspring are produced less often than 50 per cent
    • They are located on the Y chromosome, which is never inherited by offspring, so their alleles never appear in the test cross
    • They produce more recombinant gametes than non-linked genes, so recombinant offspring are produced more often than 50 per cent
    • They always assort independently, so the ratio is always 1:1:1:1 in every cross, whatever chromosomes the genes lie on

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