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1d-e, Responses to the environment & natural selection

Light-dark activity cycle of mutant mice and evolutionary implications.

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Video transcript

- [Voiceover] All right, Part D. To investigate the claim that exposure to light overrides the genetically-controlled circadian rhythm, the researchers plan to repeat the experiment with mutant mice lacking a gene that controls the circadian rhythm. Predict the observed activity pattern of the mutant mice under L12:D12 conditions and under DD, continuous darkness conditions, that would support the claim that light overrides the genetically-controlled circadian rhythm. All right, so let me write this down. So, Part D. So under some mutant mice, mutant mice, under, so let me make two columns, mutant mice under L12, L12:D12, and then under continuous, continuous darkness, what would I expect? What would I expect? So they predict the observed activity pattern. So the mutant mice, they don't have, they have some, they're lacking genes that control circadian rhythm, but under L12:D12, they don't need the genetic circadian patterns, the genetically-influenced ones, because they get the ones from their environment, the light and the darkness. They didn't get, this isn't a gene that somehow makes them not sensitive to light. So I would assume under the L12:D12, they would behave, they would have activity pattern similar to non-mutant mice, activity same as non-mutant, as non-mutant, mutant mice, non, or inactivity, inactivity during L12, activity, activity during D12. That's what I would expect. They still could react to the light and the darkness the same way that a non-mutant mice would. Now, what about continuous darkness? The non-mutant mice, we said that they, they went off of a 24-hour cycle, but they still had a cycle where they were inactive, active, inactive, active, and it was less than 12 hours for each cycle, but it was close to it. It was maybe 9, 10, or 11 hours of activity, followed by 9, 10, or 11 hours of inactivity. I would guess that a mutant mouse that has no, that doesn't have some of these genes for circadian rhythm, well, for them, it's just gonna be, it's just gonna be random, it's just gonna be much more sporadic. So, much, much more sporadic, sporadic activity, activity, fewer, fewer continuous, continuous, or I would say, maybe, less continuous periods, or shorter continuous periods, shorter continuous periods of activity and inactivity, activity slash inactivity. All right, now let's look at Part E now. So that was my predictions that I would see for mutant mice in either of these. So now let's go to Part E. In nature, mice are potential prey for some predatory birds that hunt during the day. Describe two features of a model that represents how the predator-prey relationship between the birds and the mice may have resulted in the evolution of the observed activity pattern of mice. Well, if the birds hunt during the day, if birds hunt during day a mouse is more likely to be eaten by a bird if it's active during the day. Mouse, then, then the mouse is more likely to be eaten, eaten if it is active during the day, if it is active during the day. And if it is, I guess you could say that's one, that's one feature of our model, that you're just more likely to be eaten if you're active when the birds are hunting. And then the second one is, if you're more likely to be eaten, then you're less likely to reproduce. If, actually that should be capital I, if, if the mouse is more likely to be eaten by being active during the day, then it is less likely to reproduce, then it is less likely to reproduce. And if I were, if I were taking the AP test here, I would try to put as much context as possible, because you're not exactly sure how they're, they're going to mark this thing, to grade this thing, so you could give more context that therefore, the mice that are active during, therefore, therefore, mice that are active during night, they have to be active sometime, active during night and inactive during day will be selected for, will be selected for, less likely to be eaten, less likely to be hunted, I guess you could say, and more likely to reproduce, more likely to reproduce, reproduce, and we are done.