What is the difference between phenotype and genotype?

Welcome to HealthTree University. Today we're exploring genotype, our genetic blueprint, and phenotype, how those genes show up in your body. Let's see how genes shape who you are.

What is the difference between genotype and phenotype? How does the genotype manifest the phenotype? Genotype refers to a person's genetic makeup. So you know, like we talked about, half mother, half father. But unless you're identical twins, even within your full siblings, you don't have the exact same genetic makeup, right? So the genotype refers to an individual's unique sequence of DNA. If you were to, like, unravel all the DNA that they have, that's their unique signature. So that's what resides within the cells.

The phenotype is the external manifestation of that genotype. So how that person manifests itself to the world. Can a mutation in your genotype affect your phenotype? Let's say when we're talking about genes and mutations, the genotype is the change that happens in the DNA at the DNA level that say TP53. There is a mutation in the TP53 gene. There we're looking at the genotype. If we're analyzing what's happening at the DNA level. If we're looking, we’re zooming out and we're looking at the patient, we can see what the clinical manifestations are of that mutation or of that change in the DNA. Right. So what are the phenotypic characteristics. Right. How does that abnormality manifest in the individual.

So for example, in someone who, let's say, this is very applicable for germline mutations, right, where someone is born with a mutation that predisposes them to cancer. And let's say that mutation is TP53. So that is a clinical, a known syndrome that's called Li-Fraumeni syndrome. So Li-Fraumeni patients are born with a defective copy of TP53. And that's, so again, genotypic change is at the gene level TP53. There's a mutation. Those patients will have a phenotype of essentially developing cancers at a young age, developing specific kinds of cancer. You know, that are kind of specific to TP53 as a mutated gene, right? It would be different if it was a different kind of gene that was mutated. But that is essentially, it's the zooming out and looking at the patient—that is the phenotype.

And what makes things tricky is that sometimes there are lots of variables that contribute to what kind of phenotype. You can have two people that have the same genotype. Right. They both have the mutation in TP53, but they have different phenotypes. So one manifests with a more severe form of the condition, right, with cancers happening at a very early age, and lots of clinical manifestations. And then there's more silent phenotypes, where, let's say, people live to adulthood without having developed any kind of cancer. And we don't fully understand what makes those two cases different. Right. So genotype is the same in those, but phenotype is different. So you have to look at it at both levels.

About 20 years ago we identified bases of DNA and learned that if you compare the order of those bases in you and your next-door neighbor, you two are about 99.9% identical. That is, the code of your DNA is about 99.9% the same as your neighbor who's not related to you. Well, they're kind of related to you because they're human beings. So we are related in that way, 99.9% identical, but that 0.1% is a lot of differences, because 0.1% of 3 billion is 3 million. So that means that there are over millions of bases of this code that make you different from your neighbor. And it's the idea of understanding those differences that give us a better idea of biological function.

And we refer to an individual's genome and their traits. The genome that's unique to them is their genotype. The traits that they exhibit is their phenotype, and everybody's individual—you are individually unique.

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