If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Phenotype plasticity

Identical twin astronauts, Mark Kelly and Scott Kelly, help illustrate differences between genotype (genetic info) and phenotype (observable traits). Despite their identical genotypes, environmental factors like Scott's time in space led to differences in the twins' phenotypes, showcasing the concept of phenotype plasticity. Created by Sal Khan.

Want to join the conversation?

Video transcript

- [Instructor] The folks you see in this picture are two NASA astronauts who also happen to be identical twins. On the left here, this is Mark Kelly, you can see his name on his patch right over there, and then this is Scott Kelly. And the reason why we want to look at these two astronauts in particular is to think about genotype and phenotype that we have been introduced to in other videos. So just as a bit of a review, when people talk about genotype, they're talking about the actual genetic information encoded in an organism's genes. So, if you go inside a cell we have chromosomes and then on those chromosomes, there are long, each chromosome's a long stretch of DNA. And then sections of that long stretch of DNA will code for various things, often usually various proteins. But there's a difference between what is actually, what information is in one's genes versus what actually gets expressed. The observable characteristics, that is phenotype, and two people with the same genotype they might have a very similar phenotype but they won't necessarily have an identical phenotype because above and beyond the genes affecting phenotype, you also have the environment affecting someone's phenotype. So, as you can see here, Mark and Scott Kelly, they're identical twins, they have the same genotype. But if you just look at their facial characteristics you can see that you could tell the difference between the two, and it's not just the fact that Mark has a mustache and that Scott doesn't, we could draw in a mustache, we would still see that they look different. And that's because their bodies developed in different ways based off the environment that they happen to be in. And this idea that the same genotype could result in variations of phenotype, this is known as phenotype plasticity. Phenotype. Phenotype plasticity. And maybe in one of the most extreme experiments ever conducted on phenotype plasticity, NASA was intrigued to see, well, what would happen to the gene expression if Scott Kelly spent an extensive period of time in space while his twin brother didn't. So they looked at how their bodies expressed certain characteristics before Scott spent an extended period of time in space. And then after he spent that time in space they studied his body and they saw that there was differences in the mitochondria, differences in which genes were expressed. In fact, there was a 7% difference in the gene expression after the extended time in space for Scott. So that's the example of that space environment changing Scott's phenotype. And the NASA scientists theorized that it was a low oxygen environment there was a lot of carbon dioxide in that environment, there were stressors from space travel that would have affected how the genotype which is identical to his brother, Mark's genotype, how it might have been expressed resulting in the phenotype plasticity above and beyond what other changes in phenotype between Scott and Mark accumulated over the course of their lives despite having the same genetic information.