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14. Genetic Control of Development

Studying the Genetics of Development


Genetics of Development

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Hi in this video, we're gonna be talking about studying the genetics of development. So scientists use many different types of techniques to study development. And they ask generally these there's four main questions that they ask when studying the genetics of development. So the first question is what genes control development. Right? Assuming that genes do which they do a lot of the times genes control development, we need to figure out which genes are important for proper development. And also when in development are they expressed? Are they expressed when it's just a single cell? Are they expressed when it's eight cells? Are they express when there's thousands of cells, many different stages of development? And when are these genes expressed? Um There's also where so is it a when we ask about where we can talk about two different ways we can talk about in a single cell. Is it located in a certain region in a single cell or um when multicellular organisms? Um we can say, well, you know, which sells is it expressed in? So these types of you know, when what where questions are really important? How are these genes regulated? This is a big one because much of development, like all the sales have the same genes. Right? So differences in development have to depend on how the genes are regulated when certain genes are turned on and when they're turned off And the major question that developmental scientists use to study these questions is to ask what happens if these genes are defective. So we introduce a mutation or if there's a mutation, what happens to development? Does something not develop correctly and if so what is it? And so to do to ask these questions, scientists namely use model organisms. These are organisms that have been studied for a very long time and are used to represent um the you know the genetics of development. So we study these whatever answers we get from these organisms, we hope to be able to um say that you know these exist in other organisms and even humans as well. So some examples of model organisms include yeast plants. A big one for genetics and development are fruit flies which we've talked about a lot already. Um Here's a picture of those um There's also worm C. Elegans which is really important in development because actually every single cell that this organism has um is sort of can be followed. We know exactly what it will divide into and when it will divide. It's really interesting. And then of course mice we always use mice. And model organisms are chosen because they grow easily rapidly reproduce into are genetically similar. So here's the fruit fly, here's the worm C. Elegans um Like I said before c elegans is really interesting because from the moment it's a single cell until it's a full grown adult organism, we know every single cell what it will do what it turns into when and development. It does that and how that's all regulated in C elegans. So C. Elegans is a super important organism when studying development. Now development begins with A Z. Go and this is going to be just a fertilized egg. So you know we've talked about this before. Females have eggs male have sperm for at least for humans. And so a fertilized egg is called a Z. Go. Zygotes are have a certain characteristic which is called Tony potent. And what that means is that that zygote can develop into any cell type. So when that zygote divides it can produce any cell type. It eventually produces brain cells, skin cells, kidney cells, any type of cells in the body. Right? Because it's the single cell, it it starts out and it can become anything. And so the processor which a cell becomes something like becomes a brain cell or a kidney cell is called determination. And this determination is the process to which a cell becomes committed to its faith. So what cell type is gonna be? Is it going to survive or die etcetera etcetera etcetera. Anything that this cell is going to do the process of which it becomes committed to that. So it says yes I'm gonna die or no, I'm gonna become a kidney cell. Or maybe I'm going to become a nurse cell or any of these cell types. It's called determination. Now there are two types. There's mosaic and regula tive and mosaic is what I talked about before with C. Elegans. So this is when every single cell in the organism has a predetermined fate. So you start out with a zygote and that's gonna divide and every single time and every single organism under mosaic determination, this cell will become something say kidney cell and this cell will become a brain cell. And this is a very generalized explanation of this, but this is a and then these two divide and they become something and these two divide and they become something and so on and so forth throughout all the cells in the organism. Now in every single organism, these cell divisions will happen this way these cells will become that no matter the organism, no matter what's going on in the environment, it's committed. It is saying if this cell is dividing, I'm becoming this and this and if something goes wrong and say one of the cells it dies, then there's nothing to replace it. It's either it happens or it doesn't and it happens in every organism and there's no kind of room for mistake regulated determination, on the other hand, is cells and regulate their fates according to the environment. So in this case, if you have a cell and they divide into a kidney and a brain and let's say something happens to the cell and it dies. Well when this cell divides it can compensate for that brain cell, it can make an extra copy, it can turn one of its cell divisions into a brain cell and kidney cells can't actually turn into brain cells. But I'm just using this as an example. Um it's not determining if something messes up, that's okay. Um it can fix it. If the environment, if something is screwing in the environment, it can regulate that development based on what's in the environment. So mosaic determination is very fixed. This is gonna happen, it's gonna happen in every organism and nothing can fix it. If something goes wrong, regulated regulated determination is much more um sort of floaty, you know, says, well this is what we want, this is ideal, but if something goes wrong we can fix it and it's not the end of the world. And so this this regulated is actually what happens in humans. If sells some kind of cell division thing goes wrong, some other cells can compensate for it now, like I said before development and changes in development really depends on the genes that are expressed. And so that is given a hypothesis called the variable gene activity hypothesis in this state, That determination. So that process of committing those cells to something, whether cell death or cell type is controlled through activating or inactivating genes. So that says that genes, whatever genes are expressed and whatever genes are oppressed is what's controlling that development. And so the reason that different cells become different things is because gene activation or inactivation occurs at different times and in different places in different cell types. So gene regulation is really what's controlling development. So we're going to talk about what these gene these are when they're expressed, how they're expressed and how that controls development in some of the later videos. But first I want to make sure you understand this mosaic development and regular regulated development. So let's say we start off with two embryonic cells. So these cells are both Tony potent, they can turn into anything and one cell is destroyed. So now you only have one cell in mosaic development that's going to result in abnormal development because you've lost half of the cells that you started with. And that's going to mean that half of the cells that the organism needs aren't going to be replaced. And so that's going to result in severely abnormal development. Whereas in regulated development this has a high potential of just being normal. This cell will divide or other cells will take its place and development will most likely be um unharmed because regular native development, those cells can actually make up for that missing cell. So that is the difference between mosaic and regulated. Let's now move on.

During early development, human cells determine their differentiated fates based on the environment. What term describes this phenomenon?


The variable gene activity hypothesis states that cell differentiation and determination is controlled through differences in gene activation or inactivation.


If an embryonic cell is damaged in an organism that undergoes mosaic determination, will the offspring produced develop normally or abnormally?