GCSE Biology - Meiosis #70

in this video we're going to take a look at how the process of meiosis works and at how it forms gametes now you might remember from our previous video that sexual reproduction requires gametes which we sometimes call sex cells and include things like sperm cells and egg cells the important thing about these gametes is that they only contain half the genetic material of a normal cell so we can call them haploid cells then when two of these gametes combine they'll end up forming a normal cell back and go on to grow into a new organism

and because that normal cell will have two sets of genetic information one from each parent we call them diploid cells in order to make these gametes though a cell needs to undergo meiosis which is a few different steps they need to know about first though let's just quickly recap chromosomes so there isn't any confusion if we were to take a human and look inside the nucleus of any cell we'll find these things called chromosomes which contain genetic information in fact we have 23 different types of these chromosomes in almost every cell in our body in

this cell we've only shown four to save space but just imagine that b23 like here on the right and for each of these 23 types there's actually two different copies one set is from the father shown here in blue and one set is from the mother shown here in red we can call the ones from the mother maternal chromosomes and the ones from the father pattern of chromosomes because we have 23 different types of these chromosomes and two copies of each each of our cells is going to have a total of 46 individual chromosomes getting

back to my osis the first step is to replicate all of the cells DNA by replicating all of these chromosomes this doesn't form and highly new chromosomes as such it just adds an extra arm to each of the chromosomes we already had so that they all become an X shape like this with one on being the original chromosome and the other on being the copy next these two armed chromosomes all line up along the center of the cell in their pairs so here we have chromosome one for a mother and father then chromosome two from

each parent then three and so on importantly though which one is on the left and which one is on the right is completely random so if we looked at two more cells undergoing meiosis from the same person the chromosomes in the first one might look like this and the other one like this it will always be pair one pair two pair three and so on but the left-to-right order will be random and so will be different each time and this point is actually really important because it means that in the next stage when the chromosome

pairs are pulled apart and the whole cell split in two the chromosomes are going to be randomly distributed with each half of the split cell getting a different combination of maternal and paternal chromosomes which means the DNA in each of those two cells is going to be different so so far we've doubled all the DNA and undergone the first division next we have the second division and for this the chromosomes all line up along the center of the cell again but this time is the two arms of each chromosome that are posed to opposite sides

the cell and when the cell is ready the cells didn't divide in half again leaving us now with four cells now one of the strange things to understand here is there even though a couple of these gametes might look the same they're actually all genetically unique because during the process of meiosis there are tiny changes to each of them so what we have overall is full genetically unique cells that we can call damaged and remember there are actually 23 chromosomes in each not just the four that we've shown in our example so in male animals

these would probably go on to develop into sperm cells while in females they're developed into egg cells then if a sperm and egg fused during fertilization they'd form a diploid cell that could divide by mitosis over and over again until it forms an embryo and then a fetus and then finally a fully grown organism and that's it hopefully you found that useful we'll put the link to our mitosis video in the description if you're interested and we'll see you next time