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What is a phenotype?

A phenotype refers to how an individual’s genes are expressed along with environmental influences to create traits that are visible to the eye. A phenotype also can refer to how a person’s body functions, for example, whether he or she has a certain disease.

What are examples of phenotypes?

A phenotype is the observable physical and biochemical characteristics of an organism determined in large part by their genes. Examples of phenotypes include traits such as eye color, hair color, height, freckles, and length of fingers. Phenotype also refers to traits that can be measured quantitatively such as hormone levels, enzyme activity, and blood type. 

What is the difference between a phenotype and a genotype?

A genotype is the inherited genetic makeup or code of an individual that determines what characteristics a person will express at a genetic level. Every individual has a set of genes from both parents that determine their genotype. Examples of genotypes include eye color, hair color, and certain diseases. Whereas a genotype may not be visible to the human eye, an individual’s phenotype is the summation of their genotype and are the traits that are visible or expressed outwardly. A phenotype isinfluenced by both genotype and environmental conditions. Examples of phenotypes include weight, height, blood type, freckles, and certain behaviors. 

Can a phenotype change?

A phenotype can change throughout a person’s lifetime due to environmental factors, the turning “on” or “off” of genes (known as epigenetics), and changes related to aging. Examples of an individual’s phenotype changing include weight or body size, the ability of beta cells in the pancreas to produce insulin or other hormone levels such as leptin (produced from fat cells and a factor in hunger signaling) as well as certain behaviors and conditions such as lactose intolerance.

Learn more about Phenotype:

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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