What are Alleles, Definition, Types, Examples, Function

What are Alleles, Definition and its Types:

DNA contains all the genetic information to coordinate the development and functioning of organisms. A stretch of DNA capable of producing functional RNA is called a gene. Specifically, in this article, we will understand what are allele definitions and what are their functions.

Allele Definition:

  • The two or more alternative forms of a given gene (factor) are called alleles of each other.

  • A gene located at the same position on a pair of homologous chromosomes controls the different forms of a trait. 

What are Alleles?

Allele Definition, Types Examples

  • The paternal chromosome is shown on the left, and the maternal chromosome is shown on the right.
  • These are homozygous and the same size homologous chromosomes.
  • The location of a gene on a chromosome is called a locus.
  • Two homologous chromosomes have different types of genes at the same locus.
  • In the figure, the same loci on each chromosome are indicated by dashed lines.
  • Let’s assume that the eye gene is present at this locus. 
  • At each locus, there is an eye gene inherited from the father and an eye gene inherited from the mother.
  • Alleles are the alternative forms of a given gene.
  • They occupy identical loci (positions) on homologous chromosomes. 
  • An allele is also called an Allelomorph.
  • Different alleles produce changes in genetic characteristics such as hair color or blood type. 
  • Alleles control the dominant-recessive relationships and genetic effects of relative traits and can distinguish alleles into different categories. 
  • In an individual, one form of an allele (dominant) can be expressed more than others (recessive).
  • If a pair of alleles are similar, the organism’s genotype is called homozygous. If the pair of alleles are different, the organism’s genotype is called heterozygous.

Types of Alleles:

There are mainly four types of Alleles 

  1. Wild type allele  
  2. Dominant allele 
  3. Recessive allele
  4. Mutant allele (Multiple Allele)
1. Wild type: The wild-type allele is a normal allele present on chromosomes. Wild-type allele are dominant over the other alleles.

2. Dominant allele: It is an allele that expresses its trait even in the presence of an alternative allele i.e. in heterozygous condition only. Alternatively, the allele that expresses in F1 is called dominant. (It is an allele of a pair that masks the expression of another allele in the F1 generation.)
3. Recessive allele: This allele is not expressed in the presence of an alternative allele (in heterozygous condition). It expresses only in the presence of another identical allele. It is an allele that does not express in the F1 hybrid.
4. Mutant alleles
  • Mutant alleles produce due to mutation that leads to a change in the sequence of the wild-type allele.
  • An example of mutant allele is multiple alleles.
  • More than two alternative forms (alleles) of a gene in a population occupying the same locus on a chromosome or its homolog, are known as multiple alleles. 
  • Multiple alleles arise by mutations of the wild type of gene. 
  • A gene can mutate several times producing a series of alternative expressions. 
  • Different alleles in a series show dominant- recessive relations or may show co-dominance or incomplete dominance among themselves. 
  • Wild type is dominant over all other mutant alleles.
  • An example of multiple alleles is the ABO blood group. 
Characteristics of allele:
The allele genes of a particular trait can be classified in two ways: homozygous and heterozygous.
  • Homozygous: are those that have identical gene alleles and are represented by only uppercase letters or only lowercase letters. So we can have dominant (AA) or recessive (aa) homozygotes
  • Heterozygous: are those that have different gene alleles and are represented by uppercase and lowercase letters as Aa or Bb. In this case, the characteristic that will always be manifested will be the dominant one (A) because it imposes itself about the recessive one (a)
The function of Alleles:
  • Alleles are responsible for the variations in which a given trait can be expressed.
  • Alleles determine the organism’s traits and characteristics like height, blood groups, skin pigmentation, hair, and eye color, etc.
  • One of the important functions of multiple alleles is they produce different phenotypes.

Frequently Asked Questions on Allele:

1. What does allele means?

Answer: An allele is one of two or more alternative forms of a gene, each of which is characterized by a unique nucleotide sequence; alleles usually differ in nucleotide sequences.

2. What are the different types of Alleles?


  1. Wild-type (normal) allele is the nucleotide sequence of a gene that ensures its normal operation.
  2. Dominant allele – an allele whose presence is manifested in the phenotype.
  3. Mutant allele – a mutation that leads to a change in the sequence of the wild-type allele.
  4. Recessive allele – an allele that phenotypically manifests itself only in the homozygous state and masks in the presence of a dominant allele

3. What is another word for allele?
: Allele is also called an allelomorph.

4. Where are alleles found?

Answer: Alleles are found in specific region on the chromosome called a gene locus. 

5. What is an example of an allele?

Answer: An example of alleles for plant height dominant is tall allele and recessive is dwarf allele. For flower color in pea plants the dominant is the purple allele, and the recessive is the white allele.

6. What is trait and alleles?

Answer: A trait is a specific feature or characteristic that can be passed from one generation to another, like height or hair color while alleles are the alternative forms of genes.

7. What is the function of an allele?

Answer: One of the important functions of alleles is they carry genetic information to produce different versions of the same protein.

8. What is the difference between allelic and non-allelic?


  • Alleles refer to the genes that control the same traits on the chromosomes obtained from the father and mother. For example, chickens control genes with or without earlobes. Alleles are located at the same position on a pair of homologous chromosomes.

  • Non-allelic refers to genes located at different positions on different chromosomes that control different traits, such as genes that control the presence or absence of earlobes and double eyelids.

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