Summary
More than two allelic forms of a gene exist in a population, like the ABO blood group alleles.
In depth
ABO blood group: IA and IB are dominant over i, but codominant to each other, giving genotypes AA, AO, BB, BO, AB and OO. Rabbits have four alleles for coat colour.
Each individual still has only two alleles.
The ABO gene codes for a glycosyltransferase: IA adds N-acetylgalactosamine, IB adds galactose and i gives a non-functional enzyme. Because three alleles produce six genotypes and four phenotypes, blood group genetics is used in paternity exclusion, though DNA tests are far more precise now.
Many genes have dozens or hundreds of alleles: the human leukocyte antigen (HLA) genes are the most diverse in the genome, which is why organ matching is difficult. Self-incompatibility genes in plants can have over 100 alleles.
Remember: no diploid individual can carry more than two alleles, even if the population has many.
Frequently asked questions
What is Multiple Alleles?
More than two allelic forms of a gene exist in a population, like the ABO blood group alleles.
Which area of biology covers Multiple Alleles, and how advanced is it?
Multiple Alleles is one of the 54 topics in Genetics. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Allele, Monohybrid Cross, Dihybrid Cross.
Can you give an example of Multiple Alleles?
A type A mother and type B father could have an O child if both are heterozygous (IAi x IBi).
What should I learn before Multiple Alleles?
Work through the Beginner topics in Genetics first, such as Heredity, Gene, Allele, then return to Multiple Alleles. Intermediate topics assume the Beginner vocabulary.
What topics are related to Multiple Alleles?
The closest topics to Multiple Alleles are Allele, Monohybrid Cross, Dihybrid Cross, Codominance. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Multiple Alleles?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Multiple Alleles. To practise the whole of Genetics, use the Genetics quiz.
How is Multiple Alleles different from Allele?
Multiple Alleles: More than two allelic forms of a gene exist in a population, like the ABO blood group alleles. Allele: One of the alternative versions of a gene found at the same position on a chromosome. Read both side by side and note what each one explains.
How should I study Multiple Alleles step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Allele and explain the difference aloud. Finally, take the Genetics quiz and come back to this page for any question you miss.