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Current time:0:00Total duration:7:14

Extranuclear inheritance 1

IST‑1 (EU)
IST‑1.J (LO)
IST‑1.J.4 (EK)

Video transcript

normally when we think about DNA we think about the nucleus of a cell mass because a cell's DNA is contained and it's nucleus but there are actually a few exceptions to this general rule so there are certain organelles that actually have their own DNA and two very famous examples this is the well are the mitochondria and chloroplasts so mitochondria and chloroplasts have their own DNA so I'm just going to scribble in here in blue and not only do they have their own DNA but they can actually replicate their DNA and replicate themselves independently of the nucleus of the cell in which they are so let's just talk briefly about mitochondria so mitochondria are these organelles found in eukaryotic cells and they're sometimes referred to as the powerhouse of the cell because they break down glucose to make this high-energy molecule called ATP and then the cell takes this ATP and uses it for all sorts of cellular processes and the mitochondrial DNA written like that mtDNA has about 37 genes in it and these genes most of them have to do with the cellular respiration that's going on in the mitochondria let's talk a bit about chloroplasts so chloroplasts are these organelles that are found in plant cells there are also found in algae cells and chloroplasts are the site of photosynthesis we wanted to be more specific so you have the stacks cold Granum well in singular to Granum plurals grana and those grandma are made up of these that's an M over there and those ground up are made up of these little circles called thylakoids and photosynthesis happens within these thylakoids so for during photosynthesis sunlight is harnessed of course with a bunch of other steps to make glucose so this is where the concept of making its own food comes from what's actually making glucose it's making its own food and then that glucose goes to the mitochondria of that cell and gets broken down make ATP and in the cell you decided to pay for whatever it needs to do the DNA in chloroplasts sometimes you're in CP DNA has about 100 genes and these genes also most of them have to do with proteins or things that are involved in photosynthesis and the reason that this is interesting is well let's uh let's take a look at how sexual production normally takes place we have an egg cell and the nucleus of this egg cell has only half the amount of DNA that a normal cell that organism would have so we call that N and then we have a sperm cell remember the sperm cell is really much much smaller than an Excel so this is in no way drawn to scale and the sperm cell also has a nucleus only half the amount of DNA that cells in this organism normally have so that's also n but then they fuse to make a zygote and this zygote is 2n it has the normal amount of DNA that a cell in this organism would have half of it comes from the egg cell and half of it comes from the sperm cell and then this zygote is going to divide into two cells and then those two cells of course divided further and this goes on and on until Thanks Cuse me until they are enough cells to put together an organism but this excel well it's a fully developed cell and it not only has genetic information but it has organelles in the cytoplasm so it has these mitochondria in its cytoplasm and those mitochondria have DNA in it which I'm just going to scribble some blue inside and these zygote also has those mitochondria because you remember the zygote is well practically in Excel but with the only difference being that it's nucleus has the additional DNA of the sperm cell and remember the sperm cell does not donate anything to the Excel except for half of the DNA in the nucleus it does not give the egg cell and these I go anything else so you have a zygote with that those mitochondria and of course they have their DNA in it and then when this zygote replicates itself so it replicates the nucleus but it also replicates the mitochondria in the cytoplasm and these cells will I'm going to skip out the nucleus of just drawing them out of controversy have these mitochondria but these mitochondria came only from the egg cell none of those mitochondria came from the sperm cell and so this brings us to the concept of maternal inheritance and maternal inheritance well it's basically like exactly the way it sounds it's inheritance that happens only from the maternal liner only from the egg cell so right here we're showing that the mitochondria that this organism will eventually have originates from the mitochondria that it came only from the egg cell and not from the sperm cell and therefore it exhibits maternal inheritance so both mitochondria and chloroplasts exhibit maternal inheritance because they are in the egg cell that eventually becomes the organism and maternal inheritance it's interesting to note is contrary to Mendelian genetics so maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell half from the sperm cell it does not take into account any sort of genetic information that comes from only one of the gametes for example just on the egg cell and in fact everything we just described here can be referred to as extra nuclear inheritance so extra nuclear inheritance would refer to any genes that are passed on from structures that are not in the nucleus so extra nuclear meaning outside of the nucleus mitochondria and chloroplasts are outside of the nucleus so they when they are inherited we refer to it as extranuclear inheritance so now that we've introduced action nuclear inheritance let's actually take a look at one of the early experiments that helped to discover extra nuclear inheritance