this lecture will cover meosis as well as what happens when we don't perform meosis correctly or you have any type of chromosome abnormalities um so what is meosis number one it is not mitosis it looks very similar but it's different and this is a process in which holid cells are produced from cells that are diploid um once this occurs we're going to make special cells called gamet so let me backtrack and tell you a little bit about these words words before I give you the official definition so think of a pair of socks um so let's say you have a pair of socks which would include two socks um that would be something like diploid so you see you have a pink pair a purple pair and a yellow pair all of the cells in your body for the most part are diploid meaning there are one set of chromosomes from Mom and one set of chromosomes from Dad that make you diploid 2 in okay so that is a diploid cell however when you have sperm cells or egg cells you need to split this number in half so going back to our socks this is one pink sock one purple sock one yellow sock so that when the egg comes in contact with a sperm it will end up forming a a baby that has both of the genes some from Mom and some from Dad so the process of meosis is where we take take our sets of genes our our normal genes and we split them in half to make special cells that only have half so that we can make a functional human being with the correct number of genes so a little bit about diploid and haid like I said diploid is uh refers to the chromosome number this is where a cell or a nucleus will contain two sets of chromosomes uh cells that are diploid we call those somatic cells or body cells so somatic cells is a body cell most of the cells in your body are going to be diploid or somatic um and that's going to mean it actually has 46 chromosomes so make sure that you have that number somewhere a diploid cell will contain 46 chromosomes total um and they're going to be in 23 pairs so diploid this is a human karot type and um it's going to contain 46 total chromosomes and 23 pairs of chromosomes so those are diploid cells or um somatic cells aid number is where you only have a single set of chromosomes so this is going to be your germ cell so these cells are going to be responsible for making brand new humans um and they're going to contain only half of the number of chromosomes so again a diploid cell will contain 46 chromosomes it's a complete human and for humans a holid cell will contain 23 this makes sense because when an egg and sperm meet uh the egg will have 23 the sperm will have 23 you will have 46 as the brand new embryo so uh sexual reproduction is really closely related to meosis and we'll talk about some of the benefits of um sexual reproduction as it relates to organism development so asexual reproduction is basically when a single parent can split to produce a clone asexual just means that you do not have any other type of genetic material it is literally the parent breaking apart to make a brand new clone uh bacteria do this um organisms that have very staes stable environments do it because it's very rapid very efficient so something like ecoli can replicate itself in about 20 minutes um it doesn't need another ecoli around um this is going to be asexual reproduction sexual reproduction is different it's going to be when those gametes um which are your egg or your sperm come together to form a zygote so a gamt is going to be one of the hpid or the onein cells that are going to be able to come together to form a zygote this is beneficial for us because it has a lot more genetic variation um this is helpful for Offspring so as we're trying to make better and uh bigger humans this is going to allow us to have a wide variety of genes to pull from and then it allows um adaptation to changing environment so again if we had humans that were the same as they were in 1700 they wouldn't be able to adapt to things like you know the climate currently or our nutrition and all these different aspects so having new genes introduced through sexual reproduction is going to truly benefit the growth of these organisms so let's look at a cycle of a typical human life and this is going to kind of pull in all the things we talked about with gamt sperm haid diploid all that stuff so gamt which are the eggs in the sperm are going to be haid and they are the only haid cells in the body very important gamt or the eggs in the sperm are haid meaning they're one in so you see that's just an N that's just an N this is a single sock not a a pair of socks just a single sock what happens um during feralization you have an egg and you have a sperm that come together do fertilization and they form a gamt which now has 2 N or is diploid okay so each of these gametes contributed an N or a sock if you're thinking that way so that's coming from the sperm that's coming from the egg you got 23 here here 23 here you make a diploid 2 in 46 chromosome human so the diploid number is restored we're going from haid up here but we're restoring it to diploid here and then you make a human of course as the human the little baby grows it is going to undergo mitosis because we just talked about mitosis is just pure cell division and all of the somatic cells the normal body cells will receive the same diploid set of chromosomes so once you are formed in this uh zygote you do not change your chromosomes changing chromosomes can lead to things like um some of the disorders that we have if you're exposed to radiation if they're exposed to cancer these are things that could happen once you start changing the chromosomes um so we want to make sure that we uh keep this same exact chromosome number and then as we have that our cell is going to begin to duplicate and divide as we continue to go through the mitosis process where we will eventually end up being adult males or females and then of course uh once you go through puberty and you start developing um those sexual organs you're going to undergo meosis um to form sperm and meosis to continue to develop your eggs all right so let's talk a little bit uh deeper about the meosis process and how we can create those holid cells with this really special or unique Gene combination so how we're going to do this is I'm going to basically write out or you're going to see listed out the steps of the meosis process and then we'll go back look at the picture and then kind of walk through each step one by one but this is a bird's eye view of what's happening so initially the DNA in a normal dip diploid 2 in cell is going to duplicate so now that duplicated diploid cell is going to represent a 4 in cell so we're going from two to four because we duplicate um and you can see that in this picture going from interface to replicating the DNA now we're at 4 in um once it does that it's duplicated it's going to undergo two divisions eventually leading to four haid which would you know you can write a one in here yielding four haid nuclei so down here we have the four haid nuclei you see four haid n cells so we start off with a regular 2 N cell we duplicate it to make it a 4 n cell we go through two rounds of division meosis one meosis 2 and we end up with four haid cells so so each of those haid cells contains one member of the homologus pair so here as we started to duplicate our cells they're going to have one member of each of the pairs they're going to have one pink and one blue you see here one pink one blue each homologous pair that we have is going to be special and we'll talk about that in depth but the reason they're special is they undergo something called crossing over um and I'll talk about crossing over is but crossing over is going to create a holid cell that has a very unique combination of genes so if you look right here real close you could see that even our chromosomes like for instance this one here it is mostly pink but right at the end it has a little bit of blue if you look at this one it's mostly blue but at the end it has a little bit of pink this is because we have the crossing over that occurs which I will explain in depth so the two divisions that we have um are going to be called meosis one and meosis 2 so we're dividing both our nucleus and our cytoplasm in the process of meosis one and meosis 2 each of these phases are going to include the same exact phases we covered in mitosis okay prophase metaphase anaphase telophase there are some uh specific things things that kind of happen but the concept of what occurs in each of these phases is the same so in meosis one some of the big things that happen here is those partner homologous chromosomes so uh basically like chromosomes that are really really similar homologous chromosomes they will pair and they will eventually separate into different nuclei so with meosis one the first one that happens they will pair up you see they're pairing up you have a red or excuse me a pink and a blue and then a a pink and a blue they're going to pair up and they're going to split into different nuclei so you see they've split into different nuclei and meosis 2 the sister chromatid so the sister chromatids which I will explain soon are how it has this x format each side of the X will eventually split off into a brand new cell so you see those two long blue portions here one is 100% blue the other one is blue and pink that's a sister chromatid they will split so there's the blue and pink one there is the just blue one um and that happens during meosis too okay so this is a big picture of kind of what I showed you before but just another way of looking at it and it's showing you how we naturally just have our cells right 2 in um they're going to undergo cell uh or sorry they're going to undergo replication in which you have a four in cell here um in meosis one crossing over will occur and those homologous pairs will line up at the end of meosis one you will have two separate cells that are going to have those Sister chromosomes there and then as they go through meosis 2 once you're finally done you're going to have four haid cells that can then be able to be contributed towards forming a gamet so the purpose of meosis like I talked about before is to be able to create brand new um lineages right so of course think of your family right I know you probably have a a big family or U maybe a small close family but regardless you can probably look around and see there's a lot of similarities from you know your grandparents to your your brothers and sisters to your parents everyone looks kind of similar but there are still some differences and that's good because there are certain traits that you might be better at than maybe your brother or sister is not so good at or maybe they're better at and you're not so good at but all these things are going to contribute to creating stronger human beings so before we start our meosis splits let's remind you um what happens during interphase so remember at the very first part of meosis we have to go through interphase and the s or the synthesis phase of interphase is where our DNA replicates so remember we're going from a cell that is 2 N so I I can't draw on this but it's 2 N you're replicating it so now it is 4 n so keep that in mind we're going from 2 N to now a replicated 4 n as we begin meosis 1 which is the first round of splitting for our cells we're going to start like we do with mitosis with prophase um but in this case always make sure you pay attention to the number behind it it's either going to say prophase 1 or prophase 2 so prophase one we have these homologous pairs of cister chromatids that begin to associate with each other so it's a set of four this set of four is also known as a tetrad or a B ve valent so this for instance is a tetrad this uh said this blue X and this red X this set of four is a tetrad or balent the blue X and the Red X um and each of the individual sides of the X are known as sister chromatids so imagine they you know they're right next to each other so think of them as being sisters um and then the process of when you have these four um chromatids together is just called synopsis um so I just want to kind of give you that in case you see that in your reading so in prophase one very important this is when crossing over occurs so Crossing over occurs here and it's used to create genetic variation okay genetic variation so crossing over is where we have segments of our DNA that are exchanged so we exchange segments of our DNA very critical for um developing new organisms or excuse me for developing new traits within the organism or within the lineage um and like we've done before the nuclear envelope starts to fragment in this prophase 1 stage so let me just give you another visual of what crossing over is cu it's so important this is again is a balent or a tetrad and you see here you have the red you have the green just like the holidays um crossing over is when a little portion of one sister chromatid interchanges or mixes DNA from the other sister chromatid so you end up with a organism that has um DNA from the source with a little bit of DNA from the other chromosome and then the same on this side so now when we're splitting our cells you don't have two red lines or two green lines being split um but now you have chromosomes that are all red or red and green and then some that are all green and then green and red so again that creates more genetic variability so the next step in meosis one is metaphase 1 so again very very similar terminology you're familiar with this in metaphase one um those tetrads or B veence are going to be organ organized along the middle of the cell which is a metaphase plate this will also have random arrangement of the sister chromatids what does that mean that means all the blues don't have to go on top all the reds don't have to go on top they can be flip-flop like it is here where you have a red on top in this one and then a blue on top over there that just means that's creating more variability in our new gamet anaphase you're familiar with that our homologous pairs our tetras our balence are all the same thing they're going to split and go to the opposite side of the cell so um with our telophase this is where those cister chromatids that have now split and going to the opposite side of the cell they can start to decondense that nuclear envelope will begin to form around them and the final product is going to be two diploid genetically different cells um so again our final product are these diploid cells so remember we we had a two in cell we duplicated the DNA to make it a 4 in cell and then in our first round of division we still went back to a two uh in cell so the reason we went from two to four to two is so that we can actually exchange the DNA that occurs during the crossing over stage we wanted to make sure we had an opportunity to do that and we needed to duplicate it so that we have that available however very important to notice that the DNA that we have here is going to be genetically different that's because we had this crossing over that occurred that we did not have um previously so the DNA is genetically different so again we've we've got to this point we've got pretty far in the meosis process so far we're about halfway through and here you can see that we started off with interphase which is 2 N we duplicated um during the S phase of interphase we duplicated our DNA to b4n and then as we went through meosis one we went through all the rounds we had crossing over that occurs we lined up we split apart we formed two nuclei and then we ended meosis one you know right around here in which we had two diploid genetically different cells so now we're starting up prophase 2 which is representative of meosis 2 so again meosis 2 is the second round of division so now we're going from here to here we need to finish off the rest of meosis um so again this is where we just ended right you can see that um diploid cell that has genetically different information we go through prophase one nuclear envelope dissolves metaphase they line up anaphase they pull apart telophase they form their own nuclei we do not have crossing over that occurs here we've already crossed over our DNA before um it is the almost the same exact process as mitosis um you know we follow that process the whole way but we do end up now with four haid cells okay because remember we're doing this for each of our cells so you have 1 2 3 4 we split this occurs with each of these cells that we made at the end of meosis one so meosis 2 ends up with four haid cells remember they're still genetically different from the original diploid cells that we started this process with this is just another way more detailed um item if you want to look at this that this kind of helps you to remember what's going on um just a little bit about what happens in males and females it's a little different as it relates to meosis um with our males they undergo this entire process meosis one and then they undergo meosis 2 once they are done one cell has actually split into four sperm um so you have four bable sperm with DNA um this is one of the reasons why men can produce a lot more sperm than women um they're actually able to produce uh one to four ratio so you start off with one cell and you can make four sperm that are ready to go and ready to fertilize an egg um and this happens of course as puberty begins men can continue to undergo this process up until 607 70 80 so it's it's really no time limit for men for females it's much more different when you're born you actually have a certain number of undeveloped eggs that occur or that you have in your um ovaries and your eggs are kind of developed they're they waiting and they stop they uh I think after you're born they stop right here and once you start undergoing puberty each month you're going to start to finish some of the process of meosis 2 and release that egg in your ovulation as part of your menstrual cycle but for females one cell will only equal one egg that's because we have uneven cyto Kinesis let's explain why so this first original diploid cell that we start off with it's called an noite and as it does that first round of division it normally would end in two separate cells that are even but because the egg is the place that the um embryo will grow in and all the nutrients and all of the mitochondria and other organel we talked about will be in the egg it has an uneven cyto canis so as it's splitting the internal components of the cell it starts to kind of hog or take a lot more in a lot more of the Cellular Parts in one of the eggs this little thing called a polar body eventually dissolves in your body you don't need it anymore um so as you you undergo the second round of meosis again you have uneven cyto canis so you end up forming this big Mega egg cell which has genetic information but also has a lot of organel and nutrients and things that a a baby would need is is growing inside of the egg so for females one of ourselves will only make one egg so we don't have the same luxury as um men do in which they can continue to make sperm over and over we have B basically a reservoir and after you're done with that you're done so students always find this a little bit interesting especially since we're talking about eggs and sperms and um that type of thing I wanted to talk about twins um so hopefully normally I would have asked if anybody is a twin in the room I would love to know if anybody's a twin uh because this is a little back of a little bit of a throwback um story for you so twins that are identical um what happens is that once the egg is there ready to be fertilized and the sperm interacts with with it at some point very very early in the division right so remember the egg and the sperm are haid so they're one in when they come together they form a 2in diploid organism so normally once that happens you just start developing and multiplying and then you become a little human being but with an identical twins very early in the process that fertilized egg splits into two separate um or organisms and now those separate organisms will start to develop and grow and and make make brand new babies right so then you have identical twins those twins they share the same placenta they usually share the same um amniotic sac uh all of that stuff they are literally the same egg and sperm they just split very very early in the beginning and then they started growing two separate humans twins actually have identical DNA so if one twin identical twin committed a crime and you got DNA evidence you could charge the other twin because the DNA is exactly the same so that's what happens with identical twins fraternal twins it's different um something occurs in the woman whether it's natural or um different types of medication and they have two eggs that are present in the uterus it interacts with two sperm um so that's going to create two genetically different um organisms right so it's going to be you know twin a twin b um they're going to have their own placentas it's basically like two pregnancies at one time um so this is where you have twins that are fraternal twins that are not identical U but they were born at the same time just because they were fertilized at the same time in the um in the uterus so that's essentially kind of a little bit of a story about uh twins okay so this is a really good document I would have you um just review and look look through kind of helping you to explain and understand the differences between mitosis and meosis so mitosis is regular cell division meosis is where we're making those gametes so ask yourself where at in the body does mitosis or meosis occur what are the cell types it occurs for what is the final Ploy is it hloy diploid uh what is the starting pyy of these cells what is the final number of cells and how many rounds of division do we have so you should be able to answer those comp questions as you compare and contrasted two um and this is another document from your textbook that really explains what's going on um and it's a nice comparison between um all three steps of mitosis meosis one and miosis 2 so really briefly let's talk about chromosome structure and number variation in these chromosome structures and numbers um so as you change or as you vary the chromosome structure Um this can have a really big effect on the organism a lot of different um human diseases can be affected by changing the organ the chromosome structure or number um but it has been useful for us sometimes as we evolved into new species now once an organism is set we typically don't like to have any type of changes to the chromosome number or structure um but between between species it is very common for them to be a different number of chromosomes or shapes so humans have 40 46 chromosomes but other organisms do not have 46 chromosomes and that's fine because we're different that's one of the reasons we're different so let's look a little bit about these structural changes I love this diagram because it's just very clearly talking about the different type of structural changes so imagine the alphabet A through f um some type of changes is if you have an inversion so let's say um it's supposed to of course be AB B CDE e f if you flip that CDE e you flip it right normally a b CDE e f you flip those three that's an inversion duplication two D's here insertion adding a totally another Gene from somewhere else deletion we're missing our C and translocation um that's where you're kind of flipping the chromosomes from from one pair to the next so of course it's uppercase letters here lowercase letters there in our translocation we've completely flipped these two sides of the chromosome again this is just showing more of a realistic perspective not a cartoon picture like I just showed you but there are a lot of chromosomal mutations um so when we look at a chromosome there are a few things we can identify with this chromosome um one is the size um the location of the central miror the central miror is just the um kind of The Binding agent in the middle and then banding pattern so you can kind of see it a little bit here where the dark lines versus light lines are that's known as banding pattern so as we look at chromosomes we can use any of these tools to identify them so if you have a change in chromosome number um there are a few different terms that we can use to help us identify what the change is so anytime you have something that's upy that means we have the normal number of chromosomes so for us we are diploid that means we have two in right so that is very very normal euploid means the normal number of chromosomes that's great um this is an example of a fruit fly and it shows that it has four genes here and all of them are diploid diploid is going to be two polyploid is where you have three or more sets of chromosomes so it can either be a triploid or tetraploid um so in this fruit fly you see it's a triploid instead of it being two like a diploid it is three like a triploid and then tetrol it is four and then the final one is something called anupy that's where you have an abnormal number of just a particular chromosome um so whether you're losing a chromosome or adding a chromosome you can see that in anupy so here this is naturally a diploid organism but you have an additional chromosome on the second location here and then on um when we're losing a Chron chromosome monosomy you're lost a chromosome in chromosome position three so anytime you're removing just just a particular chromosome that's anupy and this is a lot more common um especially in humans so there's a special term here called non-disjunction non-disjunction is what happens when your chromosomes do not sort properly during cell division so as we're taking our chromosomes as we're lining them up in the middle as we're pulling them apart if something happens and you pulled too many chromosomes to one side or not enough chromosomes to the other side you're going to start to get this nondisjunction um so this is going to cause um anupy gamat so as you're making those gametes you're making that sperm you're making that egg that's going to cause gamt that either have too many chromosomes like this one it's actually has one too many or it's going to have too few chromosomes depending on how well we were able to split them in those early stages so and you poyy right that means we have a too many or too few chromosomes in one of those particular um positions that's usually very lethal in animals um there's a few animals that can survive such as uh bees um especially Fe um male bees um but for the most part that's going to be lethal um there's actually about 5 to 10% of fertilized human eggs that result in um an embryo lethality so what that means is once your body recognizes um in that very very early stage of pregnancy so this could be in two weeks before uh the woman would actually know she's pregnant if your body can recognize that you actually have too many chromosomes or too few chromosomes it will naturally um abort that embryo naturally so it's not anything that's medically induced but it's just something that occurs in your body once it realizes that you have two too many or too few chromosomes in the embryo so there's some type of abnormality in the chromosome number um so actually about 50% of all natural abortions um that are due to um that are in the very very very early stages of pregnancy I'm not talking about um something later on more traumatic like miscarriages and those things but in those very early days of a pregnancy some of those can be due to alterations in chromosome number um ever there are some abnormalities that can survive so the body will recognize that it might have too many chromosomes but it it still allows the organism to develop and grow into you know a normally functioning human and those are where we have at trcm which is three chromosomes at chromosome position 13 18 or 21 and also any any of the chromosomes in the sex chromosome which are the very last chromosomes we have so again a little bit of a guide for you if um probably the most common genetic abnormality where you have too many chromosomes is Down syndrome and down syndrome is where you have three chromosomes at position 21 um and there these are some of the characteristics of down syndrome um also Edward syndrome and patau syndrome at chromosomes 18 and 13 um and then also if you have um the incorrect number of sex chromosomes this can also lead to some challenges as well so normally if females are xx and males are XY but there are a number of different disorders that can occur if you have either too many um chromosomes or too few interner syndrome uh chromosomes as well and the final closing thought as it relates to non-disjunction remember this is how your cells are able to split the chromosomes is that um Studies have shown as women age right as they starting to reach um past 35 40s 45 and up um the number of um genetic abnormalities associated with the pregnancy are starting to rise so as you age past a certain age you have higher chances now again this is still very low on this graph this is per 10,00 births you're going from 10 to 30 which is still very minimal but uh regardless your body is not as able to split apart that cell and and be able to identify and put the chromosomes in the correct location as you age um so that's why as women age as they get Beyond 35 um pregnancy can have a lot more challenges because there are usually a uh there can be some genetic um associations due to that age and the non-disjunction that occurs so that's just something to kind of help um you kind of U understand what's happening maybe around you or things you may have heard in pop culture or in life so we are done with um this portion of the lecture please rewind it please look through it if you have any questions save them and we will discuss them in class thank you