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Current time:0:00Total duration:13:54

Extranuclear inheritance 2

Video transcript

there was a scientist by the name of Carl Correns and he was a somewhat of a contemporary of Gregor Mendel he lived from 1864 to 1933 and Gregor Mendel lived from 1822 to 1884 so they were contemporaries but corns was younger than Mendel and we will soon see that Karl corns helped discover some things that do not fall into the category of Mendelian genetics so Carl Correns did a lot of experiments with this plant called the four clock plant that's how we know it which is what you're looking at I know looks a little bit like a tree but it's supposed to be a plant and actually the scientific name for the four clock plant is parabola s' Jalapa not exactly sure how to pronounce that but anyway so you did a lot of experiments with the four clock plant and one very interesting thing about this plant is that you can have within the same plant leaves there are a lot of different colors so let's say that this is the main branch of our plant and we're going to say that the leaves that come off anywhere on this branch are going to be white so there are our white leaves and we're going to say that any leaves that come off of this branch are going to be green so those are our green leaves and then the leaves that come off of this branch are variegated and that means that they have a pattern of green and white mixed so there are our variegated leaves and why is it that there are all these different colors within the plant so let's take a look at some of the cells let's take a look first at a cell that's from a leaf that's green this is in a leaf that screen so that's our cell here's our nucleus and in case you're wondering why I'm drawing the cell as a square it's because plant cells have this cell will that give it a more rigid shape and make it a bit more squarish closer to square than a circle but anyway that's our cell and this cell will have chloroplasts in it which I'm drawing as these green little circles and remember chloroplasts have their own DNA sometimes refer to as CP DNA and chloroplast DNA has in it basically the stuff that the chloroplast needs to carry out photosynthesis and one of the genes in the chloroplast DNA is a gene that makes chlorophyll which is a pigment that's involved in photosynthesis and chlorophyll is what makes the leaf green it's a pigment that turns leaf greener if you want to be more specific chlorophyll absorbs all the colors and sunlight except for green so green is really reflected but anyway the point is that chlorophyll makes the leaf green so now let's take a look at a cell that comes from a white leaf so this cell comes from a white leaf so again we'll draw our nucleus and then it has chloroplasts but the chloroplasts in this cell the DNA those chloroplasts have a mutation so the CP DNA has a mutation that does not allow it to produce chlorophyll or allows it to produce only a very very tiny metal chlorophyll because it needs chlorophyll to survive but it's not enough that the leaf will be green so I'm just going to write very very tiny amount of coral or and that's why it appears white and then the variegated leaves well they have some cells that have regular chloroplasts that meet chlorophyll and then they have some cells with the mutated chloroplasts chloroplasts with mutated DNA that do not make chlorophyll or rather make a very small amount and then they actually have a third type of cell which maybe you're guessing it already have both types of chloroplasts they have chloroplasts that do make chlorophyll and then they have chloroplasts that have mutated DNA and do not make much chlorophyll and what Cornes noticed when he crossed a whole bunch of these plants together he noticed that the progeny had nothing to do with the sperm cell or the pollen cell it had only to do with the egg cell so wherever he would take the seed from the seed is where the egg cell is located if he took it from a branch that only had white leaves all the progeny had only white leaves it didn't matter where the what the pollen cell was and the same if he took a seed from a branch that had only green leaves so all the progeny had all green leaves no matter where the pollen cell came from and this is because the treat that we're looking at the color of the leaf well that's determined by the DNA in the chloroplast and the chloroplast exhibits maternal inheritance it is going to be inherited only through the egg cell or through the maternal line or another way to say this it exhibits extra nuclear inheritance because a chloroplast has DNA that's outside of the nucleus let's take a closer look at what Carl Correns did so we have this chart to help us out and the first column we have the egg cell of the female that's the seed and then we're going to cross it with what we have in the second column which is the pollen cell that's the male gamete and they all look the same because it doesn't make any difference in our case and then we have the third calm our zygote or the result so let's look at our first row so we have this excel that came from a branch that had leaves that were only white so it came from a flower plant with only white leaves and when we cross it with a palm cell no matter what that palm cell is no matter where it came from we always get the same result we will always get a plant with only white leaves let's look at our second row so we have this egg cell that came from a branch that had only green leaves and again no matter what we cross it with no matter where the pond cell came from a white leaf of variegated leaf a green leaf or a flower of a green leaf so we always get the same result we get a plant that has only green leaves it gets a little bit more interesting when we look at the variegated at the xl's from the variegated parts of the plant because there are three different types of excels we could have we could have one that resembles the cell you see if it came from a flower with only white leaves that you then we have another excel that looks like that it looks like the excel you'd find in a plant that had only green leaves and then we have this third type of interesting cell that has a combination of the quote unquote normal chloroplasts that are green and then it has some Corp lasts that have that mutation that allowed only to make chlorophyll or make a very small amount of core so there is kind of mixed anyway let's look at a type one we cross it with a pollen cell we always get the same result we get a plant with only white leaves and then we look at Excel type two whatever we cross it with we get only green leaves and then if the Excel type three so the zygote of course will have both types of chloroplasts but remember this zygote is going to divide further and it's going to divide into four divides you know randomly divided into three different types of cells some of the cells will look like this with the chloroplasts with a mutated DNA some of them are going to look like that with the regular chloroplasts and then some of them are going to be mixed and this will give you a variegated plant some of the leaves are going to have that mixed pattern you might have some leaves that are white you might have some leaves they're green and so the bottom-line take-home message is as I explained before because the particular trait we're looking at leaf color because the gene for that trait is in the chloroplasts it exhibits maternal inheritance maternal inheritance is a type of extra nuclear inheritance just write that in parentheses because this inheritance has to do with DNA that's outside of the nucleus but anyway this exhibits maternal inheritance because it has nothing to do this particular trait is not passed down through the mail at all it's only passed down through the female and that is as we explained before because the chloroplasts are coming only from the egg cell the sperm cell does not contribute any chloroplasts to the zygote it only contributes DNA that's in the nucleus so therefore the leaf color in this four o'clock plant exhibits maternal inheritance and the same concept would apply to the mitochondria so we explain the mitochondria also has its own DNA and so if a person were to have a disease that have to do with DNA inside of the mitochondria we would know that that person got it from his or her mother and not from his or her father because the mitochondria also exhibits maternal inheritance there is one more thing about extranuclear inheritance that I want to mention and that is why is it that mitochondria and chloroplasts have their own DNA is there something that can explain that and there is the endo symbiotic theory seeks to explain why mitochondria and chloroplasts have their own DNA and this theory tells us that mitochondria and chloroplasts were once independent prokaryotes so they lived independently so of course if they're independent they need to have their own DNA but eventually they joined what I'm going to call a ancestral eukaryotic cell and in case you're wondering like when this happened we'll say about one and a half billion years ago so what happened is what happened is that the mitochondria and chloroplasts joined in ancestral eukaryotic cell and I'm going to call it ancestral because it's not exactly a eukaryotic cell that we'd see today but it's a cell that would eventually become a eukaryotic cell we could also call it a host cell because it's going to host mitochondria and chloroplasts so let's put them inside so another living in a host cell and why do you think they would want to do this so they're going to live together in symbiosis and symbiosis is when organisms look together and each one kind of gives the other something and everybody gains something so an example of this that you might have heard of is in our intestine in our gut we have the bacteria e.coli at first glance that my seem like it's not such a good thing but it's actually a really good thing because we give the e.coli a warm and cozy place to live they get some nutrients from us and in exchange they make for us vitamin K which is something very useful for us so that's an example of symbiosis each one each one or the organisms kind of tries to give something and everybody's happy so what's what's going on in the host cell so the host cell gives the mitochondria and chloroplasts a nice place to live and gives them nutrients and in exchange the chloroplast makes glucose through photosynthesis and then the mitochondria takes that glucose and produces ATP and then that ATP is used as energy the mitochondria uses some of the ATP the chloroplast uses some of the ATP and of course the host cell uses some of the ATP so everybody's happy everybody's getting something and then eventually this cell you know evolved in many different ways and of course it became the eukaryotic cell that we notice today but you know not exactly in the way it was because chloroplasts are not found in all eukaryotic cells it's basically found in plants as an algae but that's the basic idea so let's go back to the term endosymbiotic theory so endo just means inside because the mitochondria and chloroplasts began to live inside a host cell and symbiotic simply refers to symbiosis I'm just going to draw an arrow down here or first to symbiosis because each part the mitochondria chloroplasts and Hotel everybody's giving something and so this would explain why mitochondria and chloroplasts have their own DNA because once upon a long time ago they were independent prokaryotes and they lived on their own