What is an allele: Understanding Genetic Variants

An allele is one of two or more alternative forms of a gene located at a particular locus on a chromosome. Genes are segments of DNA that contain genetic information to encode certain characteristics. Alleles are variations of genes that can influence certain traits or characteristics in individuals.

Each individual has two alleles for each gene he has, one allele inherited from one parent and one allele from the other parent. Alleles can be dominant, recessive, or codominant.

  1. Dominant Allele:
  • A dominant allele will express the trait even if only one copy of that allele is present. For example, if the A allele is dominant and the a allele is recessive, individuals with AA or Aa will exhibit the trait encoded by the A allele.
  1. Recessive Allele:
  • A recessive allele will only express its character if both alleles are recessive. In the example above, an individual with aa would exhibit the trait encoded by the a allele.
  1. Codominant Allele:
  • In some cases, alleles can be codominant, meaning they express themselves equally when present together. An example is the human blood group system, where allele A and allele B are codominant.

These alleles play an important role in determining genetic variation in populations and in the inheritance of traits from generation to generation. The study of alleles and their interactions helps in further understanding of genetics and inheritance of traits in living things.


In the realm of genetics, alleles play a fundamental role in determining an individual’s inherited traits. Alleles are variations of a gene that exist at a specific location on a chromosome. In this article, we will delve into the concept of alleles, their types, and their significance in genetic inheritance.

Understanding Alleles:

An allele is a specific form or variant of a gene. Genes are segments of DNA that contain instructions for building and functioning of proteins, which ultimately determine various traits in organisms. Alleles arise due to differences in the DNA sequence of a gene, resulting in variations in the characteristics encoded by that gene.

Types of Alleles:

  • 1. Dominant Alleles: Dominant alleles are those that are expressed or observed in an individual’s phenotype, or physical appearance, even if only one copy is present. They mask the presence of recessive alleles. Dominant alleles are usually represented by uppercase letters (e.g., A).
  • 2. Recessive Alleles: Recessive alleles are only expressed in the phenotype when two copies of the allele are present. If an individual has one dominant allele and one recessive allele, the dominant allele will determine the phenotype. Recessive alleles are typically represented by lowercase letters (e.g., a).
  • 3. Co-Dominant Alleles: Co-dominant alleles are both expressed in the phenotype when present together. Neither allele dominates or masks the other. For example, in the ABO blood type system, the A and B alleles are co-dominant. Co-dominant alleles are often represented by superscript letters (e.g., IA and IB).
  • 4. Multiple Alleles: Some genes have more than two allele variants. Multiple alleles exist within a population, but an individual can only have two alleles for a specific gene—one inherited from each parent. An example of multiple alleles is the ABO blood type system, where there are three alleles: A, B, and O.

Significance in Genetic Inheritance:

Alleles are crucial in genetic inheritance as they determine the traits passed from parents to offspring. The combination of alleles an individual inherits influences their phenotype. Understanding the inheritance patterns of alleles helps predict the likelihood of certain traits or genetic disorders being passed on to future generations.

Inheritance Patterns:

  • 1. Homozygous: Homozygous individuals possess two identical alleles for a specific gene (e.g., AA or aa).
  • 2. Heterozygous: Heterozygous individuals have two different alleles for a specific gene (e.g., Aa).
  • 3. Genotype and Phenotype: The combination of alleles an individual carries, known as their genotype, determines their phenotype—the observable traits or characteristics they exhibit.


Alleles are the variations of genes that contribute to the diversity of traits observed in individuals. Understanding the types and inheritance patterns of alleles is essential in comprehending genetic inheritance and the transmission of traits from one generation to the next. Alleles play a significant role in shaping the genetic makeup and characteristics of living organisms, highlighting the intricate nature of genetics.