Life sciences · Reference
What is an allele?
An allele is one of two or more alternative versions of a gene that occur at the same position on a chromosome — the variants that account for inherited differences between individuals.
Alleles and genes
A gene occupies a specific position, or locus, on a chromosome. An allele is a particular version of that gene, differing from other versions in its DNA sequence. These sequence differences — often the result of past mutations — mean that a single gene can exist as several alleles in a population, contributing to the variety of traits seen among individuals.
Dominant, recessive and zygosity
Because most plants and animals inherit two copies of each chromosome, they carry two alleles of most genes. If the two alleles are the same, the individual is described as homozygous for that gene; if they differ, the individual is heterozygous.
When two different alleles are present, one may be dominant and mask the effect of the other, which is then called recessive. The combination of alleles an organism carries — its genotype — together with the environment shapes its observable traits, or phenotype.
Significance in research
Alleles are central to genetics, from Gregor Mendel’s original studies of inheritance to modern analysis of genetic variation across populations. Cataloguing which alleles exist, how common they are, and how they relate to traits is a major task of genomics. Consistent identifiers for variants and alleles are essential so that findings about a given allele can be compared and reused across studies.
Key facts
At a glance
- Definition: an alternative version of a gene at a given locus
- Origin: differences in a gene’s DNA sequence
- Number per gene in diploids: two (one from each parent)
- Homozygous: two identical alleles
- Heterozygous: two different alleles
- Dominant vs recessive: describes which allele’s effect is seen
Common questions
FAQ
What is an allele in simple terms?+
An allele is one of the different versions of a gene. Because a gene can vary in its DNA sequence, the same gene can exist as several alleles, which is why individuals inherit different forms of a trait.
What is the difference between a gene and an allele?+
A gene is the unit of heredity at a particular position on a chromosome. An allele is one specific version of that gene. An organism typically inherits two alleles of each gene, one from each parent.
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