Lesson 6.1.2a

6.1.2a Variation and genetic diagrams Quiz: OCR Biology, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6.1.2a, Variation and genetic diagrams: 20 multiple choice questions for the OCR Biology (H020), Unit 7: Genetics and evolution, written with Revision Ninja.

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The 20 questions

  1. What phenotypic ratio is expected from a monohybrid cross between two heterozygotes?

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

  2. What phenotypic ratio is expected from a dihybrid self-cross with independent assortment and complete dominance?

    • 3:1
    • 9:7
    • 9:3:3:1
    • 1:1:1:1 only

  3. What term describes plants becoming pale and elongated when grown in total darkness?

    • Chlorosis
    • Dwarfing
    • Phototropism
    • Etiolation

  4. Why are males more likely than females to show X-linked recessive conditions?

    • Males are homozygous
    • They have two X chromosomes
    • Y chromosomes carry the allele
    • Males are hemizygous

  5. Which term describes a pattern of inheritance where both alleles are fully expressed in the phenotype?

    • Incomplete dominance
    • Recessive inheritance
    • Codominance
    • Epistasis

  6. What term describes an interaction where one gene masks the phenotypic expression of another gene?

    • Epistasis
    • Linkage
    • Codominance
    • Polygenics

  7. Which two processes during sexual reproduction generate new allele combinations in offspring?

    • Meiosis and mitosis
    • Meiosis and fertilisation
    • Translation and transcription
    • Mitosis and fertilisation

  8. In a cross Aa x Aa, what proportion of offspring are homozygous recessive?

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

  9. In a dihybrid cross AaBb x AaBb, what proportion of offspring are aabb?

    • 1/16
    • 9/16
    • 3/16
    • 1/4

  10. A monohybrid cross gives 84 dominant and 36 recessive offspring from 120 total. The expected ratio is 3:1. What is the chi-squared value?

    • 1.6
    • 6.0
    • 0.4
    • 2.4

  11. A cross between a group AB parent (IAIB) and a group O parent (ii) is made. What is the probability that a child has group AB?

    • 1/4
    • 0
    • 1
    • 1/2

  12. A female carrier (XAXa) has children with a normal male (XAY). What is the probability that a son is affected (XaY)?

    • 0
    • 1/2
    • 1/4
    • 1

  13. A dihybrid testcross produces mostly parental phenotypes with few recombinants. What does this indicate?

    • Dominant epistasis
    • Autosomal linkage
    • Recessive epistasis
    • Independent assortment

  14. A dihybrid cross yielding a 9:3:4 phenotypic ratio is characteristic of which genetic interaction?

    • Dominant epistasis
    • Duplicate epistasis
    • Complementary epistasis
    • Recessive epistasis

  15. What combination of sex chromosomes in human parents produces a 1:1 sex ratio in offspring?

    • XX and XX
    • XX and XY
    • XY and XY
    • XO and XX

  16. A dihybrid testcross yields 8% of each recombinant phenotype. What is the total recombination frequency?

    • 16%
    • 42%
    • 84%
    • 8%

  17. A chi-squared test yields a value of 0 when testing a 3:1 ratio. What is the correct conclusion?

    • Accept null hypothesis
    • Reject null hypothesis
    • Genes are linked
    • Data is invalid

  18. Why do epistatic interactions alter the expected 9:3:3:1 dihybrid phenotypic ratio?

    • Non-disjunction
    • Phenotypic classes merge
    • Failed gamete fusion
    • Gene mutation

  19. Why is a female less likely than a male to express an X-linked recessive disorder?

    • Only affects Y chromosomes
    • Needs two recessives
    • She is always immune
    • Has no X chromosomes

  20. An affected male (XaY) has children with a woman who is homozygous dominant for the trait (XAXA). What proportion of their daughters are carriers?

    • 1/4
    • 0
    • 1/2
    • 1

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