2.5.1 Monohybrid inheritance and pedigree diagrams Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 2

The 20 questions

1. In monohybrid inheritance, what term describes an allele that is expressed in the heterozygote?

   • Lethal, because it prevents the individual from developing to adulthood
   • Dominant, because it masks the effect of the recessive allele in the heterozygote
   • Codominant, because both alleles are always expressed equally in every cell
   • Recessive, because it is hidden in the heterozygote and only shows in homozygotes

2. What is the expected phenotypic ratio in the offspring of two heterozygous parents for a single gene with complete dominance?

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

3. A test cross is used to find out whether an individual showing a dominant phenotype is homozygous or heterozygous. What is the test cross?

   • Crossing the individual with a heterozygous individual
   • Crossing the individual with a homozygous dominant individual
   • Crossing the individual with a random individual from the population
   • Crossing the individual with a homozygous recessive individual

4. In incomplete dominance, a red-flowered plant is crossed with a white-flowered plant and all the offspring are pink. What is the expected ratio from a cross of two pink plants?

   • 3 red : 1 white
   • 1 red : 2 pink : 1 white
   • 9 red : 3 pink : 3 white : 1 pink
   • 1 red : 1 pink

5. In a pedigree diagram, how is a female individual usually represented?

   • A triangle
   • A diamond
   • A square
   • A circle

6. In a pedigree, two unaffected parents have an affected child. What does this indicate for the condition?

   • The condition is recessive and both parents must be carriers
   • The condition is dominant and both parents must be homozygous
   • The condition is caused by a dominant allele on the Y chromosome
   • The condition is X-linked dominant in every case

7. What does the term 'genotype' mean?

   • The alleles an individual carries for a particular gene
   • The chromosome on which a gene is located
   • The sequence of amino acids in a protein
   • The observable characteristic produced by an individual's genes

8. In a pedigree for an autosomal recessive condition, which pair of parents could produce an affected child?

   • One heterozygote and one homozygous dominant parent
   • Two homozygous dominant parents
   • One affected parent and one unaffected homozygous dominant parent
   • Two carriers (heterozygotes)

9. Two heterozygous parents for a recessive condition have a child. What is the probability that the child is a carrier but not affected?

   • 3/4
   • 1/2
   • 1/4
   • 1/8

10. A pedigree shows an autosomal dominant trait that appears in every generation. What is the chance that an affected parent who is heterozygous has an affected child?

    • 50%
    • 25%
    • 100%
    • 75%

11. In a monohybrid cross between two heterozygotes, what proportion of offspring are homozygous recessive?

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

12. A dominant allele A and recessive allele a control a plant trait. A heterozygote is crossed with a homozygous recessive plant. What is the phenotypic ratio of the offspring?

    • 3 dominant : 1 recessive
    • 1 dominant : 1 recessive
    • All recessive
    • All dominant

13. A geneticist finds that 25% of offspring from a cross between two carriers show a recessive phenotype. Which ratio does this match?

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

14. A cross between a dominant homozygote (AA) and a recessive homozygote (aa) gives F1 offspring. What is the genotype of all F1 offspring?

    • Equal numbers of AA, Aa and aa
    • All Aa
    • Half AA and half aa
    • All homozygous dominant (AA)

15. A pedigree shows an unaffected pair of parents with two affected daughters and one unaffected son. What is the most likely inheritance?

    • Y-linked, passed from father to son only
    • Autosomal dominant, with both parents homozygous recessive
    • X-linked dominant, with the father affected
    • Autosomal recessive, with both parents as carriers

16. In a pedigree, a shaded symbol represents what?

    • An individual who is a carrier of a recessive allele
    • An individual who has died
    • An individual who shows the condition or trait
    • An individual who was not tested

17. In a monohybrid cross with incomplete dominance, what phenotypic ratio results from the F2 generation of pink x pink?

    • 3 red : 1 white
    • 1 red : 2 pink : 1 white
    • 1 red : 1 white
    • 2 red : 2 white

18. Which of these terms refers to a pair of alleles that are the same at a locus?

    • Heterozygous
    • Mutant
    • Dominant
    • Homozygous

19. A pedigree shows a condition that skips a generation, with unaffected parents and an affected grandchild. Which inheritance pattern is consistent with this?

    • Autosomal dominant, because every generation must show the trait
    • Mitochondrial, because the trait passes from father to child
    • X-linked dominant, because the trait must pass through males
    • Autosomal recessive, because carrier individuals can pass the allele on silently

20. Two heterozygous parents have three children. What is the probability that all three children are affected by a recessive condition?

    • 1/16
    • 1/64
    • 1/4
    • 3/64

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