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GCSE Biology · key term
Describes an allele that is expressed in the phenotype when at least one copy is present.
Used by AQA, Edexcel and OCR
Specification 4.6.1.6 · Paper 2
Revise: Key Vocabulary and Principles of Genetic InheritanceImagine a single-gene model in which red flowers are controlled by a dominant allele R and white flowers by a recessive allele r. A plant with RR or Rr has red flowers; a plant with rr has white flowers. These pairs of letters are genotypes, while red and white are phenotypes.
Specification 3.11B, 3.13 · Paper 1
Describes a hereditary factor whose effect is expressed when paired with a recessive factor.
For a single-gene characteristic, use the same letter in upper and lower case for its dominant and recessive alleles, such as R and r.
A heterozygous organism still carries the recessive allele even when its phenotype shows the dominant characteristic.
Do not assume every characteristic follows a simple dominant–recessive pattern: most involve several genes.
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He distinguished dominant and recessive factors. In these flower-colour crosses, the factor for purple flowers was dominant: its effect appeared when it was paired with the factor for white flowers. The white-flower factor was recessive: its effect was masked in the first generation, but it could still be inherited and appear in later offspring.
An allele whose characteristic is expressed when just one copy is present in a pair.
Specification B5.1a · Paper 2 (Foundation), Paper 4 (Higher)
An allele that produces its associated phenotype when one or two copies are present.
Revise: Genetic terms‘Dominant’ describes the observed phenotype of the heterozygous plant; it does not mean that one allele removes the other.