Difference between Dominant and Recessive Alleles

Updated on June 28, 2018

Many of our characteristics are considered to be things we inherit from our parents. For example, we often hear people say that we have our mother’s eyes or our father’s nose. This all boils down to genetics. Our DNA is made up of genes. The differences in people’s traits are due to the variations in our genes. These varying genes are called alleles. There are two types of alleles: the dominant and the recessive. In this article, we’ll discuss the differences between dominant alleles and recessive alleles.

Summary Table

Dominant AllelesRecessive Alleles
Dominant phenotypes will manifest when either or both chromosomes have the same dominant alleleRecessive phenotypes will only manifest when both chromosomes have the same recessive allele
Designated by a capital letter when expressing the genotype notationDesignated by a small letter when expressing the genotype notation

Definitions

brown eyes
The trait of having brown eyes is an indication that a dominant allele is present

A dominant allele is the type of allele that is expressed when it is present in either or both of the two chromosomes in the pair for a specific gene. In other words, the phenotype associated with the allele manifests the dominant trait whether both chromosomes have the same copies of the dominant allele (homozygous dominant) or if just one chromosome contains the dominant allele (heterozygous dominant).

blue eyes
The trait of having blue eyes is an indication that two recessive alleles are present

A recessive allele the type of allele that will only be expressed if both chromosomes contain the same copy of the recessive allele for a particular gene (homozygous recessive). If a recessive allele is inherited together with a dominant allele, only the dominant phenotype will manifest.

Dominant Alleles vs Recessive Alleles

The main difference between dominant and recessive alleles is on how they manifest as physical or behavioral traits. They are also written differently in terms of genetic notations.

Alleles are variants of a particular gene. People, as well as most animals and some plants, are diploids, meaning they have paired chromosomes. A particular gene would have a copy on each of chromosomal pair. These genetic pairs may or may may not be exactly the same. If the alleles are the same, they are described as homozygous. If they are different, they are called heterozygous.

The composite of the characteristics we inherit from our parents that manifest as physical or observable traits is called a phenotype. Hereditary eye color, skin pigmentation, hair color, height, and behavior are just some examples of phenotypes. The phenotypes are partly determined by the alleles present in our DNA.

Dominant phenotypes will manifest when either or both chromosomes have the same dominant alleles, whereas recessive phenotypes will only manifest when both chromosomes have the same recessive alleles.

We often designate dominant alleles with a capital letter and the recessive allele with the corresponding small letter. For example, the dominant allele for brown eyes may be designated by the capital letter “B” while the recessive allele from blue eyes may be designated by the small letter “b.” The brown eye phenotype may be of the genotype BB (homozygous dominant), Bb, or bB (heterozygous dominant). Notice that the heterozygous genotypes do not manifest as blue eyes even if the recessive allele associated with blue eyes is present since the dominant allele for brown eyes is present. In order for the blue eye phenotype to be manifested, the genotype must be bb, where both carry the blue eye recessive allele.

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