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What is an allele?

An allele is the version of the gene that is present at a specific location in the chromosome. Each person has two alleles for each gene, one from each parent. If the alleles of a gene are the same, the person is homozygous for the gene. If the alleles are different, the person is heterozygous for the gene.

What is a dominant allele?

In genetics a dominant allele is the variation of the allele that is expressed as the phenotype even when other alleles are present. In other words, it masks or hides the expression of the other allele (known as the recessive allele). Having brown eyes is an example of a dominant allele. An individual only needs to have one copy of the allele that encodes for brown eyes, the one copy of the brown eye allele will mask or dominate the effects of any allele that codes for a different eye color.  

What is the difference between an allele and a gene?

A gene is a specific unit of DNA or genetic material which is located on a chromosome and is responsible for how certain traits are expressed, such as eye color or freckles. Individuals inherit one copy of a gene from each parent resulting in a total of 2 copies of each gene. Each copy of the gene is not exactly the same from each parent. An allele refers to the specific variation between the copies of the same gene and may result in differences in how a phenotype, or gene is expressed, such as having blue eyes versus brown eyes.  

What is a recessive allele?

A recessive allele is a type of allele that will not be expressed when there is only one copy of this particular gene variation present, it will be masked or hidden by the other allele present. A recessive allele will only affect expression of a gene or trait if both copies of the gene are the same recessive allele. 

Learn more about Allele:

Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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