The size and shape of the vertebrate skull can reveal a great deal about an animal's lifestyle and evolutionary relationships. Consider your own skull. If you put your finger in your ear and move your jaw up and down, you can feel the space near the hinge of your jaw. Nestled in this space are the tiny bones that make your hearing possible: the malleus, incus, and stapes. All mammals have these three ear bones, but reptiles such as this T. rex don't. Where did ear bones come from? Researchers studied mice embryos as a model organism to determine whether the cells of the ear bones originated from the same embryonic cells as the cells that form the jaw in other vertebrates. Why would the researchers use mice instead of humans? Do the results from mice tell you something about your own ears? Why or why not?

Video transcript

Welcome back. Let's look at our next question. The gene that includes encodes retinoblastoma. RB protein is a conserved gene in plants and animals, this gene has primary control over whether the cell continues to divide or to differentiate when it is activated. RB represses the gene required to replicate the DNA. Which the following happens when RB is inactivated in the stem cells of vertebrates. So to keep this straight here, let's remember that R B activated represses jean required to replicate DNA, it's not there. This has the effect of stopping cell division. The cell cannot proceed to the S. Phase of the cell cycle because it cannot replicate the D. N. A. That's part of that step. So we're looking to say what would happen when the RB is inactivated. Let's say cell division continues, The cell cannot replicate its DNA move onto the S. Phase and then proceed through the cell cycle. When we look over our answer choices, we see that all of them involve um questions of whether the cell is going to stop or continue dividing and whether they differentiate. So we want to look back at what our question told us and where it mentioned differentiation. And so in our question it says the gene has primary control over whether the cell continues to divide or to differentiate. So this is kind of key. The cell continuing to divide means it will not differentiate. So that's important to understand. So cell division continues the cell will not differentiate. So we want to keep that straight here. So with that in mind let's look at our answer choices, Choice A says the stem cells stop dividing and differentiate. Well, as we noted here, when RB is inactivated, which is what our questions asking about cell division continues. So Choice A. Is not our answer. Choice B says the stem cells continue to divide. Well that is what we see. So we'll go ahead and highlight that. Choice. C says the stem cells will divide and differentiate at the same time. Well, we know that inactivation of RB will call cell division to continue and as we saw it means it will not differentiate. So Choice C. Cannot be our answer choice D. Says the stem cells will stop dividing and differentiating well division continues. So Choice D. Is not our answer. So which of the following happens when RB is inactivated in the stem cells of vertebrates. Choice be the stem cells continue to divide. See you in the next video.