BRAINCAKEMultiple Alleles
So far, genes have had only two alleles. Some genes have more than two alleles in the population. These are called multiple alleles.
Each diploid individual still carries only two alleles of the gene, one on each of a pair of homologous chromosomes. The extra alleles exist in other members of the population.
The ABO blood group gene
The gene I controls an antigen on the surface of red blood cells. It has three alleles:
• IA gives antigen A
• IB gives antigen B
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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.
- dominance hierarchy
- An order of dominance among multiple alleles of a gene, in which each allele is dominant to those below it and recessive to those above.
More in Genetics and Variation
- Species
- Allopatric Speciation
- Sympatric Speciation
- Artificial Selection
- Codominance
- Codominance Genetic Crosses
- Multiple Allele Crosses - ABO Blood Groups
- Autosomal Linkage and Recombinant Offspring
All 41 lessons in Genetics and Variation · All AQA A-level Biology topics