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Gene vs Allele: Definition, Difference and Comparison

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Article

Gene vs Allele: Definition, Difference and Comparison

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Genes and alleles are essential to basic genetics, but what are the differences between them? In this guide, we compare genes and alleles and provide simple definitions and examples for both.

What is a gene?

Genes are sections of DNA that determine certain traits or characteristics. Genes encode for proteins that influence things like the immune system, skin pigmentation, hormone production, and eye color. 


Genes are inherited from an offspring’s parents, and they are responsible for features being passed down from one generation to the next. An organism’s genotype consists of its entire set of genes. Every human has a unique genotype, which explains the vast variety in human appearance and biology.

What is an allele?

When genes mutate, they can take on multiple forms, with each form differing slightly in the sequence of their base DNA. These gene variants still code for the same trait (i.e. hair color), but they differ in how the trait is expressed (i.e. brown vs blonde hair). Different versions of the same gene are called alleles.

Genes can have two or more possible alleles. Individual humans have two alleles, or versions, of every gene. Because humans have two gene variants for each gene, we are known as diploid organisms.

The greater the number of potential alleles, the more diversity in a given heritable trait. An incredible number of genes and gene forms underly human genetic diversity, and they are the reason why no two people are exactly alike.

As an example, let’s look at eye color. In a simplified model, we will assume that there is only one gene that encodes for eye color (although there are multiple genes involved in most physical traits). Blue, green, brown, and hazel eyes are each encoded by unique alleles of said gene. The pair of alleles present on an individual’s chromosomes dictates what eye color will be expressed.

How are genes and alleles inherited?

When humans procreate, the child receives 23 chromosomes (long strands of DNA) from each parent. Each matching chromosome pair contains the same set of genes, with unique genes located at certain spots known as the gene locus.

This inheritance means that individuals have two gene copies for a given trait, one inherited from their mother and the other from their father. These are known as maternal alleles and paternal alleles. It is how these alleles interact that is responsible for unique characteristics.

What is a dominant gene and what is a recessive gene?

The totality of genes encoded on a human’s 46 chromosomes is known as their genotype. But not all gene variations will be expressed. For instance, you might have one allele for brown eyes and another for blue eyes, but you will not therefore have one blue and one brown eye.

Individuals do not display the characteristics encoded on each matching pair of genes. Instead, the genes that are expressed result in the phenotype, which is how genes are expressed in observable characteristics.

How does the body know which alleles to express? This comes down to the properties of alleles that are paired.

Every individual has two copies, or alleles, or a single gene. When the alleles are the same, they are known as homozygotes. When they are different, they are called heterozygotes.

Homozygotes code for the same trait, for instance, blue eyes. If you have two blue eye alleles, your eyes will be blue. But if you have one allele for blue eyes and another for brown eyes, your eye color will be dictated by whichever allele is dominant.

A dominant allele is one that always determines the phenotype when present. On the other hand, a recessive allele is one that is not expressed when its paired allele is dominant.

With eye color, the brown eye allele is dominant to the blue eye allele. This means that a child with a blue allele from their mom and a brown allele from their dad will end up with brown eyes. But a child with two blue alleles will display the blue eye phenotype.

Gene vs allele: chart

Gene

Allele

Definition

A section of DNA that encodes for a certain trait

A variant form of a gene

Role

Genes determine individual traits

Alleles contribute the diversity in phenotype expression

Determines

An organism’s genotype

An organism’s phenotype

Number per genus locus

One

Two

Various Types

Alleles

Paternal vs maternal

Dominant vs recessive

Examples

Eye color, hair color, skin pigmentation

Blue eyes, brown hair, dark skin

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