Alleles — Definition & Role in Inheritance

The Difference Between a Gene and an Allele

Imagine that you're a scientist working with frogs. You have two frogs: one green and one blue. If you wanted to describe these frogs to someone, what kind of genes would you say the frogs have?

In the case of the frogs, they have the same set of genes, but they have very different alleles. Both frogs have skin, which means they both have genes for skin development. However, the specific type of gene, which determines the color of the skin, is known as an allele. So, one frog has the green skin allele and the other has the blue skin allele, but both frogs have a gene for skin.

These terms often seem interchangeable. You might say that you have the genes for brown or blonde or red hair. However, that is more properly referred to as having different alleles. An allele is just one specific way that a gene can be physically expressed.

They are also important when talking about genetic disorders. That's because while one allele of a gene might code for a completely normal trait, another one might cause a disease.

Gene vs. Allele

In a basic allele relationship, one dominant allele and one recessive allele. Only the dominant one will be physically expressed.

However, keep in mind that this is just a simplified version of what actually happens. Often, things get more complicated when we encounter things like codominance, incomplete dominance, or polygenic traits.

What Is an Allele?

They are different forms of a gene. They code for different variations of the same trait. Green, blue, and brown eyes are alleles of the gene for eye color. Curly or straight are alleles for hair type. The picture below illustrates this. All of the beverages in the picture are the same type but have different flavors.

For every gene, you inherit one allele from each parent. So, in total, you get two versions of each gene. Some alleles are dominant and some are recessive. This is known as the Law of Dominance, one of Mendel's laws of inheritance. An organism with at least one copy of a dominant trait will display that form of the trait. Recessive traits only appear when there is no dominant trait present.

A really neat example of this is your earlobes: if your earlobes are attached, congratulations, you have a recessive trait. If your earlobes are free, you display a dominant trait.

Why Do We Study Them?

Each person can only have two alleles, but there may be multiple ones for a given trait within the population. This is why there is so much diversity among humans and among members of different species. Geneticists study allele frequencies to see how different versions of given traits are spread out throughout populations, and how this changes over time. They can also use diagrams, like Punnett squares and pedigrees, to see how different traits are passed on over many generations.

$$\color{#8925ae}{\text{Vocabulary Review:}}$$

$\color{#8925ae}{\text{Chromosome}}$ : A chromosome is a long, single, coiled piece of DNA

$\color{#8925ae}{\text{DNA}}$ : The macromolecule that stores all of an organism's genetic information

$\color{#8925ae}{\text{Gene}}$ : A DNA sequence that codes for a specific trait or protein

$\color{#8925ae}{\text{Allele}}$ : Genes of the same type that contain different kinds of information

(Video) Genes vs. Alleles

by 2 Minute Classroom

In this video, 2 Minute Classroom explains the difference between genes and alleles.

Each of your cells contains two sets of chromosomes—one set from Dad and one set from Mom. Therefore, your body has two copies of each gene. The two copies are not identical because your parents are not identical. The slightly different versions of the same gene are called alleles.