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Current time:0:00Total duration:11:49

Video transcript

if organisms have to reproduce then in previous videos we've seen that the cells need to be able to make a copy of themselves which means that the DNA of a cell must be able to make a copy of itself now if you're not familiar with this we've talked a lot about this in great detail in a previous video called reproduction in DNA but the important thing to note here is that a DNA copy is never 100% perfect so the way I've shown over here is as an example I have changed the color of this line from green to purple just to show you that it's not hundred percent perfect so in this video we're gonna try and explore a little bit as to why this is not hundred percent perfect and then we will see what is the consequence of this what does it mean for reproduction that's what we're gonna explore in this video so let's start with the why part why does this happen why can't DNA make a perfect copy of itself well the answer is actually quite simple its errors in copying these are what what we are seeing over here are basically errors in copying and to give you a little bit more you see in order for DNA to copy itself DNA first of all is a very long molecule and if you want to make a copy of itself then there are tons of biochemical reactions that need to take place right and the thing is chemical reactions are not always 100% perfect so something or the other might go wrong somewhere and because simply errors are definitely possible in our world chemical reactions are not always perfect because of that and there are so many chemical reactions are happening for DNA copying put all of them together and you will find that the copies will not be 100% perfect it's kind of like your friend is trying to copy the recipe to cook pasta now he or she may be writing everything were toward or trying to write everything were toward in her own book but occasionally she might make some mistakes she might skip some words or she might skip some sentences not purposely but maybe she would do that and a result if you look at the copy that your friend has made well it's pretty much still the same recipe it is still going to cook you pasta itself but there might be some changes happening in that recipe so now this brings us to the question what happens because of this what is the consequence of this DNA error in copying well to talk about that let's get rid of these pictures and now let's think about what are the consequences well if you look at short term maybe there are no consequences for example when your friend is copying the recipe of that pasta maybe she misses some of the words maybe she maybe she copies some words wrong but still maybe the recipe is still exactly the same the ingredients used are still exactly the same and so the pasta that she will cook will pretty much be the same as the pasta you will cook so remember your DNA is a recipe to cook not pasta but to cook proteins or not to cook but to make proteins synthesized proteins and so even with small errors here and there maybe the proteins made by this new copy of the DNA would be the same as the proteins made by the old cop all DNA and so in that case your offsprings will look pretty much identical to your original self things may not change however as you keep me more making more and more copies as you keep making more and more errors there could be some critical errors that you might make for example maybe one of your friends or cousins you know people who loved cooking around you may be one of them when they're making a copy of this book maybe they make a mistake in the amount of milk to be added maybe the originally the amount of milk to be added was I don't know maybe 9 liters but that person makes it by mistake 8 liters ooh now that person's pasta is going to change a little bit it's gonna it's gonna taste may be a little bit different compared to the original so you see that pasta will have some changes compared to the original one and so we say there will be some variations similarly when organisms reproduce because of the errors that are happening in the DNA sometimes the error can be critical and because of that the proteins built could be different altogether and as a result that individual could have some variations so the of these errors in the copying of DNA is it leads to variations in some organisms and so I guess now the million-dollar question is are these variations good or bad well it depends upon how you look at it in short in short here's the thing if you look at it from an individual point or point of view for individual organisms individuals we will say variations can be good can be good we'll take examples or it can be bad or it can be bad both are possible or maybe it will be harmless like we said before sometimes it can be hard as harmless as well so for individuals it could be good bad or it could be harmless but for the species if you're looking for the species as a whole variations are definitely good in fact I'll go ahead and say that if you want a species to survive over a long period of time maybe millions of years you need to have variations variations is the key for the species to survive why am I saying that let me take an example to make this clear consider a species of bacteria living in water at 27 degrees Celsius let's say that these bacteria have adapted for that particular temperature this temperature is perfect for these bacteria then we will say that this particular water at this particular temperature has become the niche has become the niche for the bacteria think of niche as a well-defined space this water 27 degrees Celsius for which the organisms are perfectly adapted for okay just to give you a more relatable example think of cactus the cactus also live in a very well-defined place where temperatures are pretty high during the daytime no water for a long time basically a desert and the cactus has developed or has a Tapp did for that particular condition so we can say the desert forms the niche for this cactus okay so basically think of niche as a well-defined space for which that particular organism has adapted itself all right now of course it turns out niche is a very broad concept a lot look at it in great detail just think of it as a well-defined space for now alright so what will happen well these bacteria will thrive in this particular environment and so they will reproduce more and increase its population and they will occupy that niche we will say but now let's think about the variations every bacterium will have some or the other variations because of the errors in the DNA copy some of these variations might be good or some of these variations might be harmless for this particular niche so these bacterias will just keep on living and keep on reproducing they will not be affected by these variations but what if there are some variations which are bad for the bacterium let's say one of this particular bacterium has a variation this one has a variation because of which it can live only in higher temperatures not 27 degree Celsius but it is adapted for higher temperatures let's say then what will happen well because it is not perfectly adapted for this particular niche it might die or maybe because it is not very very well suited we might find it may not reproduce much whatever it is you can see this bacterium is at a disadvantage and so that's the reason why I said for individuals variations can be good or they can be bad because these variations are happening randomly right so it can be good or it can be bad but let's think from the species point of view why is it good for species well there are a couple of reasons one is you see for good the individuals which have good variations that's great for the species they will they will be able to reproduce and grow in number great for the species but if you consider the individuals that have bad variations maybe they will die or maybe they won't reproduce much and that's fine that's fine because their numbers will reduce but our other ones which are thriving so the ones that fit in this particular environment will keep on reproducing more and more so you see the species as a whole is not affected by bad variations right so variation berry variations do not affect the species okay that's one reason the second most important reason though of why variations are important is because niches can change and that's important this can change so just to give an example what I mean over here is the temperature of the water will not always remain 27 degree Celsius forever maybe as time passes by after a few thousands of years we find the temperature of water is rising it's rising because of global warming let's say now as the temperature is rising now what happens now we will see that these bacteria are at a disadvantage because they're adapted for 27 degree Celsius but this particular variation now has an advantage right because that is adapted for higher temperatures and so what will happen now well now as time passes by we will see the numbers of these guys will start decreasing but the numbers of these ones will start increasing because they are better adapted because but they had better adapted to that new higher temperature environment and as a result we will now find this one increase in number and so you see what has happened the species has adapted to that change in H and so variations and love or prepare the species to adapt itself in case the niche changes and that's the reason why variations are super super important for species to survive in fact guess what without variations good chance that you and I wouldn't even exist because think about it the earth has gone through so many changes there was a time where the entire earth was covered with ice we call that his ice age then there was a time when earth got hit by the meteor so many drastic changes have happened so many changes in the niche has happened then the only way life could survive was due to random variations random variations gives the species a chance to survive all right so to summarize what did we learn in this video we learned whenever organisms reproduce their DNA makes a copy but there can be errors in these copies and as a result the offsprings will have some variations if you look at individuals relations can be good or they can be bad some variations might have a disadvantage in that particular niche but for the species as a whole the variation is good because Nicias can change and just to recall what's a niche you can think of niche as a well-defined space for which the organisms have adapted themselves