Inheritance & EvolutionDefinitions

Key Definitions

Part of Genetic Inheritance · GCSE GCSE Biology revision

This definitions covers Key Definitions within Genetic Inheritance for GCSE Biology. Genetic inheritance patterns, alleles, and inheritance diagrams It is section 4 of 9 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.

Topic position

Section 4 of 9

Practice

26 questions

Recall

12 flashcards

Key Definitions

Dominant allele: An allele that is expressed in the phenotype whenever it is present, even if only one copy is inherited. Written with a capital letter (e.g., B).

Recessive allele: An allele that is only expressed in the phenotype when two copies are present (homozygous recessive). Written with a lowercase letter (e.g., b).

Homozygous: Having two identical alleles for a gene (e.g., BB or bb). A homozygous dominant individual (BB) and a homozygous recessive individual (bb) will both breed true for that characteristic.

Heterozygous: Having two different alleles for a gene (e.g., Bb). The dominant allele is expressed in the phenotype, but the recessive allele is still present and can be passed to offspring.

Genotype: The combination of alleles an organism carries for a particular gene (e.g., Bb, BB, or bb). Genotype determines what phenotypes are possible.

Phenotype: The physical or observable characteristic produced by the genotype, e.g., brown eyes (BB or Bb) or blue eyes (bb). Phenotype can also be influenced by environmental factors.

Punnett square: A grid used to predict the possible genotypes and phenotypes of offspring from a genetic cross, based on the gametes produced by each parent.

Carrier: A heterozygous individual (Ff) who carries one recessive allele for a condition but does not show symptoms, because the dominant allele is expressed. Carriers can pass the recessive allele to their children.

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.

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

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.

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How It Works: Dominant and Recessive Alleles

Common Misconceptions