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Genes, traits, and the environment

Environmental factors affect expression of traits, and hence affect the probability of occurrences of traits in a population. The variation and distribution of traits observed depends on both genetic and environmental factors. Created by Sal Khan.

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Video transcript

- [Instructor] This is a prize-winning Himalayan rabbit, and it will help us see that an organism's traits aren't only the results of which genes they have, but also which environmental factors the organism is exposed to. So we're gonna look at a specific gene in the Himalayan rabbit known as the C-gene, and to C-gene encodes a protein which acts as an enzyme in the eventual production of pigment. And we can see where that enzyme is more active, at the nose, on the feet, on the ears right over here, and then you could also see that it is inactive across the body and in some parts of the head right over here. Now the question is what's causing it to be inactive or active? Well, it turns out that the enzyme that the C-gene codes for is optimally active at 15 degrees Celsius to 25 degrees Celsius, and this alone can actually explain the difference in pigmentation. How does that make sense? Well imagine that this rabbit over here was raised at 20 degrees Celsius. The body itself, it's a mammal, it's warm blooded, it's going to be producing heat. So the body, this area right over here, is going to be warm. And so, over here where we're going to be greater than, let's say 35 degrees Celsius, where the enzyme that the C-gene and codes for is inactive. This is where it's optimally active, and above 35 degrees Celsius it's actually not active at all. And once again, why is it so warm over here? It's not just the ambient temperature. It's the combination of the ambient temperature plus the heat from the rabbit itself. Now, if you go at some of the further off parts of the rabbit's body, and this is actually true of our bodies as well, if you go to the ears, you go to the nose, you go to the feet, you have less body warmth. And so, it is going to be cooler in these parts of the body, and it could be cool enough so that the protein encoded by the C-gene is actually active. And so, you see something very simple can create this very neat and, I would have to say, cute pattern as well. Now, some of you might be wondering, well, could I then based on temperature, raise a completely white Himalayan rabbit, and the answer is yes. If you had a twin of this rabbit and you raised it in an environment that was, say, hotter than 30 degrees Celsius, well then all of its body would probably be of a temperature where the protein encoded by the C-gene is not too active or not active at all, and it would be a white rabbit. And people have performed this experiment over 100 years ago and they saw that exact result. And temperature is just one of many factors. So there's research where they're able to make a Cyclops fish, a fish with one eye, based on chemicals and where it was reared. There's experiments with the light that depending on the light or the lack of light, at the caterpillar stage, it can affect what the butterfly looks like when it develops wings. Food can activate or inactivate certain genes, not just in other animals, but even in our own bodies. There's research around fasting and how that might activate or inactivate certain genes. Stress can affect genes. Hormones can affect genes. So the big takeaway here is an organism's traits are not just due to which genes the organism has, but are influenced by environmental factors as well.