Summary
One of the alternative versions of a gene found at the same position on a chromosome.
In depth
Diploid organisms carry two alleles per gene, one from each parent. A population can hold many alleles, though an individual carries at most two. Alleles arise by mutation and differ by as little as one base.
Allele combinations determine genotype and, with the environment, the phenotype.
Alleles differ by single base changes (SNPs), insertions, deletions or repeat numbers. Wild-type is the common allele in nature, and mutant alleles can be loss-of-function, gain-of-function or dominant-negative. Many human variants are neutral, and only a minority have effects.
Allele frequency in a population shows evolution in action: the sickle cell allele reaches 10 percent or more in parts of Africa where malaria is common, because carriers resist the disease. Alleles can be traced as haplotypes, blocks inherited together.
Common mistake: confusing allele with gene. A gene is the locus, and alleles are the versions at that locus.
Frequently asked questions
What is Allele?
One of the alternative versions of a gene found at the same position on a chromosome.
Which area of biology covers Allele, and how advanced is it?
Allele is one of the 54 topics in Genetics. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Penetrance and Expressivity, Test Cross, Genetic Drift.
Can you give an example of Allele?
The gene for human ABO blood type has three common alleles: IA, IB and i.
What should I learn before Allele?
Allele is a Beginner topic, so no earlier topic is required. Other Beginner topics in Genetics that pair well with it include Heredity, Gene, Genotype and Phenotype.
What topics are related to Allele?
The closest topics to Allele are Penetrance and Expressivity, Test Cross, Genetic Drift, Dominant and Recessive. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Allele?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Allele. To practise the whole of Genetics, use the Genetics quiz.
How is Allele different from Penetrance and Expressivity?
Allele: One of the alternative versions of a gene found at the same position on a chromosome. Penetrance and Expressivity: Penetrance is the fraction of carriers showing a phenotype; expressivity is how strongly it appears. Read both side by side and note what each one explains.
What is a common mistake about Allele?
Confusing allele with gene. A gene is the locus, and alleles are the versions at that locus.
How should I study Allele 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 Penetrance and Expressivity and explain the difference aloud. Finally, take the Genetics quiz and come back to this page for any question you miss.