The world knows James Watson as the legendary scientist who unlocked the secrets of the DNA molecule. He once said, “We used to think that our fate was in our stars, but now we know that, in large measure, our fate is in our genes.”

While our genes heavily affect our fate, have you ever wondered how they express and determine our traits? If you recall my lectures, you might remember two words I have frequently mentioned: the genotype and the phenotype. But what exactly do they refer to?

Read on to brush up on your understanding of the genotype and phenotype!

Genotype and Phenotype

What is Genotype? Definition and Example

The genotype refers to the genetic makeup of an individual. A living organism’s genotype determines how different traits or physical characteristics emerge. However, remember that just because a particular gene is present in an individual, it may not necessarily be expressed!

This sounds contradictory – if our genes determine our physical traits, how is it possible that our characteristics may be different from what genes we have? But it’s a relatively simple concept to understand once you remember that environmental factors also determine our traits! For example, a person may have genes that make it possible to have a tall height, but if they don’t get the proper nutrition, they may not be as tall as their genes have fated them to be!


A real-life example of genotype:

Let’s understand this concept with the help of an example. Take the case of the human blood types: humans have four distinct blood types: A, B, AB, and O. If a person has the genes for the blood type A, their red blood cells (RBCs) express the antigen A, while if they have the blood type B, their RBCs express the antigen B. Some individuals have the genes for both A and B blood types, and they express both antigens, resulting in an AB blood group. It’s also possible that they express no antigen, which happens when they have the O gene. The gene sets A, B, AB, and O represent the person’s genotype.

A person gets one gene each from their father and mother, so they have two copies of genes for each trait. These different copies are called alleles. If one gets a copy of the A gene from each of their parents, their genotype will be AA, and they will have the blood type A. Similarly, if they receive the A gene from one parent but the B gene from the other, their blood type and genotype will be AB.

But what happens if they get an A gene from one parent and an O gene from the other? That’s where it gets interesting! The person’s genotype will be AO, but their blood type will be A, as the O gene does not express if the A gene is present. This example illustrates how the genotype is different from the physical trait. For a better understanding of this scenario, make sure you have already studied about monohybrid and dihybrid crosses.


What is Phenotype? – Definition and Example

Phenotype refers to the expressed physical trait of the person. Their genotype determines what phenotype they will have. Remember that the relationship between phenotype and genotype is complex, and having a particular genotype does not necessarily mean that its corresponding phenotype will be expressed.

While the genotype comes from a person’s genes and cannot be changed, some phenotypes do not remain constant throughout life as environmental factors affect them. For example, a person’s weight changes throughout life depending on diet and exercise. However, not all phenotypes can be changed, for example, the natural eye color or the shape of your ear lobes.

If we look back at our previous example of blood groups, an individual expressed four distinct phenotypes: A, B, AB, and O. The phenotype is determined by their genotype, but the same phenotype can be due to different genotypes! For example, a person can have the blood group B due to the genotype BB or BO.


Differences between Genotype and Phenotype

While the genotype and phenotype are similar concepts, the two have several essential differences. We will draw a table of these differences so that you can easily understand the differences between the two terms.

DefinitionThe genetic makeup of a personThe physical traits of a person
NatureInherent and fixedDynamic and malleable
Effect of EnvironmentNo effectEnvironmental factors can influence the phenotype
ObservabilityNot directly observable; genetic tests and punnet squares are required to determine the genotypeDirectly observable
DeterminationInherited from parentsComplex interplay between genetic and environmental factors



Both the above mentioned topics are essential concepts in genetics, and understanding the difference between the two is critical for understanding genetics. While the two terms sound similar, there are crucial differences between them.

Think of the genotype as the genetic blueprint for an organism and the phenotype as how the blueprint manifests. While the phenotype depends upon the genotype, environmental factors can influence it at any stage of life. By understanding this subtle difference, you can grasp genetics better!

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