BRAINCAKECodominance
Most genes you meet first show dominance: in a heterozygote, only the dominant allele is expressed in the phenotype. Some genes behave differently.
Codominance occurs when both alleles of a gene are expressed in the phenotype of a heterozygote. Neither allele is recessive, so the heterozygote has a third, distinct phenotype.
Because neither allele is dominant, codominant alleles are not shown with a capital and a lower-case letter. Instead, a letter represents the gene and a superscript represents each allele.
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Key terms in this lesson
- allele
- One of two or more alternative versions of a gene, occupying the same locus on homologous chromosomes.
- genotype
- The genetic constitution of an organism, i.e. the particular combination of alleles it possesses.
- phenotype
- The observable characteristics of an organism, resulting from the interaction of its genotype with the environment.
More in Genetics and Variation
- Species
- Allopatric Speciation
- Sympatric Speciation
- Artificial Selection
- Codominance Genetic Crosses
- Multiple Alleles
- Multiple Allele Crosses - ABO Blood Groups
- Autosomal Linkage and Recombinant Offspring
All 41 lessons in Genetics and Variation · All AQA A-level Biology topics