Edexcel GCSE Biology

Inheritance & Punnett squares

Edexcel GCSE Biology revision on Inheritance & Punnett squares. Aligned to the Pearson Edexcel GCSE Biology 1BI0 specification. This bank has 5 practice questions on this topic.

Sample questions (3 of 5)

  1. Question 1

    Which statement correctly describes the genetic makeup of an individual who is homozygous recessive for a specific trait?

    • A) Two identical dominant alleles
    • B) Two different recessive alleles
    • C) Two identical recessive alleles
    • D) One dominant and one recessive
    Show answer

    Answer: Two identical recessive alleles

    The term homozygous indicates that the two alleles for a gene are the same. Since the trait is recessive, the individual must carry two copies of the recessive allele to express the phenotype.

  2. Question 2

    If a heterozygous parent (Aa) is crossed with a homozygous recessive parent (aa), what is the probability of the offspring being homozygous recessive?

    • A) Twenty-five percent chance
    • B) Fifty percent probability
    • C) Seventy-five percent odds
    • D) Zero percent likelihood
    Show answer

    Answer: Fifty percent probability

    By setting up a Punnett square with 'Aa' on one side and 'aa' on the other, you produce four possible combinations: Aa, Aa, aa, and aa. This results in a 2/4 or 50% ratio for the homozygous recessive genotype.

  3. Question 3

    What is the term used to describe the physical expression or visible characteristics of an organism's genetic makeup?

    Show answer

    Answer: phenotype

    While the genotype refers to the specific combination of alleles an organism possesses, the phenotype is the actual physical manifestation of those genes. This includes visible traits like eye colour as well as internal physiological characteristics.

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