Inheritance & EvolutionKey Facts

Punnett Squares

Part of Genetic Inheritance · GCSE GCSE Biology revision

This key facts covers Punnett Squares within Genetic Inheritance for GCSE Biology. Genetic inheritance patterns, alleles, and inheritance diagrams It is section 2 of 9 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 2 of 9

Practice

26 questions

Recall

12 flashcards

Punnett Squares

A Punnett square shows possible offspring from two parents:

Example: Eye colour (Brown = B, Blue = b)

Parent 1: Bb (heterozygous brown)

Parent 2: Bb (heterozygous brown)

	B	b
B	BB	Bb
b	Bb	bb

Result: 3 Brown (BB, Bb, Bb) : 1 Blue (bb) = 3:1 ratio

Probability of blue eyes: 1 in 4 = 25%

Visual: Punnett Squares and Genetic Crosses

Punnett square diagram showing key genetic terms, genotype vs phenotype, examples of Bb x Bb and Bb x bb crosses with 3:1 and 1:1 ratios, and step-by-step guide to drawing Punnett squares

Remember: Bb x Bb = 3:1 phenotype ratio | Bb x bb = 1:1 ratio | Dominant allele (capital) masks recessive (lowercase)

Keep building this topic

Read this section alongside the surrounding pages in Genetic Inheritance. That gives you the full topic sequence instead of a single isolated revision point.

Key Terms for Genetics How It Works: Dominant and Recessive Alleles Key Definitions Common Misconceptions

Practice Questions for Genetic Inheritance

What is the term for an allele that is always expressed when present?

A. Recessive allele
B. Dominant allele
C. Homozygous genotype
D. Recessive phenotype

1 markfoundation

What is the purpose of a Punnett square in genetic inheritance?

3 marksstandard

Quick Recall Flashcards

What is a recessive allele?

An allele that is only expressed when two copies are present (homozygous recessive). Represented by a lower-case letter (e.g. b). It is 'hidden' by a dominant allele.

What is a dominant allele?

An allele that is always expressed in the phenotype, even if only one copy is present. Represented by a capital letter (e.g. B). Think of it as the 'bossy' allele.

26 questions on Genetic Inheritance — practise free

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Key Terms for Genetics

How It Works: Dominant and Recessive Alleles