Illustration showing dominant and recessive alleles for hair traits, including hair color, hairline, and hair texture.

Diagram of dominant and recessive alleles affecting hair color, hairline, and texture.

Allele

Category: General Biology Date: November 13, 2024

What is an Allele?

An allele is a variant form of a gene that can cause different traits in an organism. Each organism inherits two alleles for each gene, one from each parent.

Dominant and Recessive Alleles

Dominant and recessive alleles are different versions of a gene that determine how a trait will show up. Alleles come in pairs because we inherit one from each parent.

A dominant allele is stronger and usually shows up in the phenotype, or physical trait, even if there’s only one copy. For example, if brown eyes are dominant, then a person with one brown eye allele and one blue eye allele will have brown eyes. The dominant allele “covers up” the recessive one, so only the dominant trait appears.

A recessive allele is weaker and only shows up if there are two copies of it. This means both parents need to pass down the recessive allele for the trait to appear. For instance, blue eyes are recessive. A person will only have blue eyes if they inherit a blue eye allele from each parent.

So, dominant alleles are strong and show up even with one copy, while recessive alleles need two copies to be seen. Together, dominant and recessive alleles determine how many traits appear in people and other living things.

Statistics

Alleles are different forms of a gene, and in humans, there are many interesting statistics about them. For example, let’s look at eye color. Brown eyes are dominant, which is why about 79% of people worldwide have brown eyes. In contrast, only 8% of people have blue eyes, and that’s because blue is a recessive allele and requires two copies to show up.

Hair color is another interesting example. Brown hair is also dominant, so about 75-80% of people have brown or black hair. Meanwhile, blonde hair, which is recessive, shows up in only around 2% of people worldwide.

Another fun fact is about blood type. Blood types can be A, B, or O, with A and B being dominant over O. This is why around 44% of people have type O blood, as both parents need to pass on the O allele for it to show up. About 42% have type A blood, and 10% have type B blood, while only 4% have type AB blood.