we are live welcome back to year two of the MCAT lecture series we did this whole introduction yesterday unfortunately yesterday the first chapter biology the uh the video wasn't working and then we had to figure out like a whole roundabout way to have the lecture live streamed by the way we have a live stream for the lecture now join the WhatsApp chat and I'll also leave the link for the live stream um in the description of the YouTube channel as well it will be until further notice every Tuesday and Wednesday at 6:30 p.m. Eastern Standard Time if you want to come in person the lecture is at 2310 ingersol Hall at brooken college right same time obviously because I'm live streaming the lecture um now if you want all this information at your fingertips as well as all the information that I have to offer you for the mccat you can go to the description of this video and you will find a link to a Google drive folder and in that drive is a link to the sign up form for the email where I send all the important uh updates and you'll also find my study guide which is a basically goal designated approach about how to study for the MCAT um in the description you will also find a link to the WhatsApp chat which you can join if you want to hear us talk a lot but also get updates on the Fly um and you'll also find a link to my buy me a coffee page if you want to support the channel in any way possible you don't have to it's certainly a very nice thing to do uh but also 50% of all proceeds go to charity um I actually just took the withdrawal out of my account for the past couple months so you guys will be getting an email about our donation to Doctors Without Borders very soon um what else is in the description uh obviously a link to the zoom sessions that is a permanent link because I now have a unlimited Zoom account that I use for uh tutoring and this lecture and think that's about huh the study gues in the drive folder yeah so you can go there and you can also find all my notes and everything like that um if you guys are new this is all the information you need to be completely honest um but unfortunately I'm so sorry that the recording didn't work too well for the first day um but that's why we're here and everyone who's sitting in the room right now this is the second time you're getting the you're getting the introduction so I apologize for that but for the people on YouTube Welcome and or welcome back by the way who did the homework from yesterday and told a friend about this program you did perfect so everyone who's watching right now your homework if you haven't done it already is to tell one friend about this program so that we can grow organically and more people can benefit from the stuff that we put out what are we covering today what are we covering today we are covering chapter two of General biology and like I said before in the room before we began uh chapter two of General biology is one of the hardest chapters in all of the MCAT in general like it is it is one of the most difficult chapters of MCAT knowledge you'll ever study but that's why you have me and we're going to walk through it slowly and we will do some chatting and talking and everything as we go along and we'll have a good time right that's what we're here for we're here to have a good time and obviously become doctors and all that stuff that's secondary though right okay so chapter two general biology is reproduction reproduction also people on YouTube we have a new setup there's a chalkboard here instead of whiteboard I'm trying to get that changed I miss my whiteboard but the chalkboard does kind of make me feel cool um so bear with me for I don't know I don't know how long we'll have this for but hopefully not forever anyways reproduction so like I said before this chapter goes into a lot of things that um you know Encompass a lot of the chapter before it so obviously the cells so we talk about cellular reproduction but we also talk a little bit about sexual reproduction and what leads up to the formation of an actual new human being because if you remember from discussion about cell theory for something to be living we need it to be able to reproduce right and cellular reproduction and human reproduction are two completely different things if we reproduce like cells that would be really weird because I would not want 17 of me running around all over the place that' be kind of freaky right so let's talk about Chapter 2.1 the cell cycle and mitosis cell cycle and mitosis okay so as a definition we already talked about what a cell is but what is an autosomal cell what does this word autal mean h not necessarily what does autosomal mean it means a nonsex Cell It's a nonsex cell it's it's not a cell that's going to be active in the reproduction of the organism correct okay so what are sex cells called gametes good sex cells are what we call gametes very good or they're also called germ cells because of cies obviously okay so germ cells now autosomal cells are what we call 2 N they have a 2 N genome whereas germ cells have an N genome meaning that the total number the total number of chromosomes what are chromosomes they're pack little packages of DNA right that make up the genetic material of a cell in an autosomal cell it's double the amount as it is for a germ cell and in a germ cell it's basically all of the genetic material that is required for the organism to survive right but there's only one copy of each so let's talk about reproduction before we get any further right so you have a cell in your body right and let's say that you are an organism and you only have three chromosomes total right so you have one chromosome that looks like this and you have another chromosome that looks like this you have another chromosome that looks like this right so 1 2 3 but do you see how you have two copies of each that is what we mean by 2 N you have two n chromosomes and N is the number of chromosomes that's within your entire genetic file so for you it'd be three so it's 2 * three which is six but if this guy were to make a sex cell for reproduction right it would split off and it would actually only make one with I this is too small for Zoom chat one with three chromosomes but what's going to happen is this guy's mate is also going to make a cell with three chromosomes and when they come together they're going to make a 2 N cell and that's how the basics of reproduction happen right so those are the basics that an N cell and an N cell become a 2 N cell and that's why sex cells are n and AAL cells are 2 N right so that makes sense let's explore a little bit further so you carotic cells go through this thing called the cell cycle right why I write a G1 after G1 is what s after s is G2 after G2 is M then G1 right and M is actually a very very small sliver of the cell cycle the rest of it is a lot larger right and this guy M actually stands for mitosis so what is mitosis mitosis is actually the process of cellular division to make two identical daughter cells listen I don't know about you but if my daughters look like me I'm freaking out right that'd be weird two identical daughter cells right so if you are a human and you have a 23n genome Nal 23 and you have an autosomal cell how many chromosomes are in this cell an autosomal cell 46 you have 46 chromosomes 23 of them are from Mom and 23 of them are from Dad right so you have two copies of chromosome 1 two copies of chromosome 2 two copies of chromosome 3 until you get two chromosome 22 and then what about chromosome 23 what's the 23rd pair of chromosomes the sex chromosomes right so if you're female it's going to be XX or if your male it's going to be X Y correct but it's still two chromosomes so it's still 2 N unless of course there's something wrong which we're going to talk about later okay quick question quick Jolly Rancher question let's get it rolling Let's uh speed up the race a little bit what's the most common chromosomal abnormality seen in humans who actually survive Down syndrome and what's the medical name for Down syndrome anyone anyone trii 21 you have three copies of chromosome 21 does anyone know the average age of onset of Alzheimer's and people who get it it's around 65 to 70 right let's call it 68 people with Down Drome actually develop Alzheimer's if they get it by age 40 why does that happen well it's because the 21st chromosome actually has the gene for something known as ameloid protein it has ameloid precursor protein the AP Gene and since people with Down Syndrome have three copies of this instead of two they produce a lot more ameloid and if they produce more ameloid there's a higher chance of that ameloid becomes messed up and then that messed up amid causes Alzheimer's disease so Alzheimer's is a big comorbidity comorbidity of down syndrome as are congenital heart defects things like atrial seple defects that patient that I saw pass away yes uh not that I told you guys about yesterday I saw a patient pass away in the Pediatric emergency department um you know a while back um that patient actually had Down syndrome and uh died after a surgery that they had to repair a heart condition all right so we're going to break down some of these cell cycle points G1 stage so the G kind of stands for Gap and this is known as The presynthetic Gap the presynthetic Gap the cell increases in size increases the number of organel increases efficiency right all getting ready for this synthesis phase which is the answer of course to what does the S stand for after G1 right and basically what you're doing is you're constantly sort of producing a more favorable environment for the synthesis of what synthesis of DNA right DNA the synthesis of DNA because if you're going to split into two cells that look like you you have to double your genome correct so that's what we're going to talk about in a bit you guys having fun yet oh by the way since we have the microphone and the air you guys can turn on the fan because they're not going to hear it unless none of you wants to get out I mean the Fan's right there it's over there um Okay so the passage into the S phase from the G1 phase because we're going to go from G1 over into the S phase now obviously the S phase is where we're going to make the DNA and if the DNA is you know important to how the how the um cell is going to divide it wants to be restricted correct you're not just going to let any cell in any way move on to the S phase right so this right here is our first what we call restriction Point people in Zoom chat if you can hear the fan in the earbud please let me know I hope you can't it's pretty far away it is pretty loud but the thing is we we had fans on like in the lecture hall downstairs and I don't think the microphone picked it up uh but I guess good but I guess we'll see when I rewatch this lecture by the way I don't know how you guys do it I've never sat through a single one of my lectures like I've never watched one of my own lectures from top to bottom I've never done it like it I I've told myself I was like oh you know like I should watch this just to see if I made like mistakes or you know like uh what's it called no turn that away from me so I'm like oh I should watch this cuz I want to know if I made mistakes or like you know how does my hair look at this specific scene or whatever like checking to see if I like leaked my address by accident or whatever I've never watched a single one of my lectures throughout ever I maybe watched like five minutes of my lecture continuously just doesn't happen oh yeah so the S phase basically what's going to happen is that let's say well we'll get there obviously but it's going to be the synthesis of DNA because if you have something that has let's say two chromosomes and you want to create two identical copies of this thing you can't not replicate the chromosomes because you have to have in the end you have to have how many chromosomes four correct so sometime somehow you need to go from two to four and then split into 2 by two right it's like that old game of Chopsticks you used to play as a kid you guys remember that right okay so that's the S phase you're getting ready for the synthesis of DNA that's going to take you to this 2N from 2N to 4N right because you're doubling that's how variables work oh my god look math okay so after the G1 phase where we're growing our organells getting things ready for synthesis right we're going to begin the S phase but not before we pass through a restriction point and a restriction Point basically goes around the cell and goes okay this check this check this check if you've ever been on a road trip or a trip with friends you one of your friends is the Restriction point it's like oh my god did everyone bring the charger and the backpack and the sleeping bag and this and that and packs 17 changes of clothes for a 3-day trip there's that's the that's the Restriction point it's making sure that every single thing is absolutely perfect so that when you move on you don't need to go back because there is no going back right because once you've moved on you are now officially in the S phase the synthesis phase cells replicate genetic material so let's consider an organism that has one chromosome this organism has one chromosome correct in the S phase the chromosome is going to look like this right and when you progress further and you actually synthesize the DNA the chromosome is now going to look like this right and I always thought that it was this part that was continuous with this part like it's going diagonally it's not it's like being pinched if you can imagine it it's like two things standing side by side that are being pinched together so this part is actually continuous with this part right okay so what are these two things called sister what sister chromatids right so this is a chromatid and this is a chromatid and these are known as sister chromatids no James Charles right s chromatids what is the thing that connects them I always forget which is why I just looked at my laptop cental or Centro close Centro miror it's called a centrom this is why I forget it there's so many Centro things and I just like the least self-centered person right okay so this is what happens inside of the S phase so let's say that your n you know just for the sake of it I'm going to draw a second chromosome you guys don't have to and I'm going to do an opposite this one and this guy is going to turn into that so let's say your n was two or sorry your n was one so you have one chromosome you have a pair of those chromosomes right this is actually a better example because now it's a pair right you have a pair of those chromosomes so your two n number is two but when you replicate how much chromosomal information do you actually have you have double that you have 4N but what gives gives how do you how do you have 4N right what happens is that here this n is single stranded this is 2N single stranded this is 4N double stranded or technically 2 N double stranded and then it becomes 4N single double does that make sense and if this were to split to go into meiosis that would be single stranded n Right double stranded n makes 2 N double Stranded 2 N makes 4N does that make sense Okay cool so after the S phase right we're almost moving on to the m phase which is where we're going to do our dividing correct so we go G1 s G2 M correct so now we're here the post synthetic Gap the post synthetic Gap so this is basically just one thing and one thing only quality control quality control so cells checking to see if we have enough DNA if the DNA is properly made if the daughter cells are going to have enough organel in order to live right if we have enough for the daughter cells in general that's what this is all about quality control right and the cell make sure that there are no errors in DNA replication does anyone know the gene protein that we use in order to do that very welln very wellknown genan the moment I say it you're going to remember it's p53 it's p53 p53 for Gan editing and checking any questions from Zoom chat yeah can you show us the diploid numbers in terms of the human genome 23 46 and 96 yes I will in a moment we'll get there hold your horses mitosis no my sister didn't step on my toe we're talking about mitosis cell division right so let's go back to our one chromosome organism so in the time from G1 to G2 it started out like this and then it became this right so this is our n or 2 n two copies of the one chromosome that's in this organism and now it's a double stranded version of those two copies so this is 2 N double stranded which makes 4N does that make sense so now this guy is under going to undergo a process and there's multiple steps here so first is prophase so this is step one of mitosis right type one of mitosis so prophase means that the DNA condenses and the cental pairs separate so the cental separate these are the guys that are going to move to the edge of the cell and throw the spindle fibers later we'll talk about that in a second right just thinking how I want to approach the rest of this one more thing the nuclear membrane dissolves the nuclear membrane disappears so the cell is going to look like this when you start those are the cental that's the cental pair this is all the DNA and at the end it's going to look like this so the nuclear envelope is gone the chromosomes have condensed and now these cental are moving to the opposite ends of the cell and by the way this isn't an original thing this is a diagram straight out of Kaplan you can find it so if my drawing isn't doing it for you you can definitely find this diagram I'm not a great artist it's why I'm here teaching you guys metaphase these chromosomes are going to meet up in the middle of the cell at what called the metaphase plate metaphase plate runs straight down the middle of the cell and the kineticore or sorry the the cental are at opposite ends it dissolves oh so the nuclear membrane nuclear membrane dissolves and one more thing is that the spindle fibers are thrown and help the chromosomes to line up so what does that look like we have the chromosomes like this and then these centrioles are here here and they throw fibers to help these guys line up and that place where they attach to the chromosome that's called a kinor whether or not you'll see that on the MCAT n unlikely everyone following so far cool so let's count that diploid number we were talking about before so over here we have 2 N here we have 2 N double strand that's 4N right so for humans this is 23 or sorry this is 46 because it's 2 * 23 46 over here this is your 92 you have 92 single strands of chromosomes arranged in 46 double stranded right sorry single strands of chromatids arranged in 46 double stranded chromosomes does that make sense damn it is dry in here this used to give me the biggest goddamn headache of all time when I was in college oh my God it's so annoying and then you start learning about like in medical school you start learning about like non-disjunction errors to like a deeper degree and you learn about like the genetics of different uh chromosomal abnormalities and diseases and you're just like ah that's not that bad everything becomes not that bad when you're in medical school because that's the only way you can cope because if everything was that bad then you drop out can't be doing that all right what's after metaphase anyone know anaphase so this is step three of what mitosis right so some people actually forget they're just like oh well like what are we talking about here we're still talking about mitosis just has multiple stages anaphase what happens to anaphase the sister chromatids split they get divorced what am I dumb hold on oh yeah so they're getting pulled in opposite directions right towards opposite ends of the P of the cell it's kind of all you need to know about anaphase just this uh the spindle fibers are pulling them in opposite directions Zoom chat any questions all right twois these two this is Prem mitosis this is getting ready for mitosis so this is your interphase and what is interphase it is the collection of G1 s and G2 did anyone just see that move that was creepy that was weird this little screen just moved on top of me I was like what the hell it so weird okay and then finally what's the last step of mitosis tase or telophase right the spindles break down so number one the spindles break down the nuclear membrane reforms bilaterally what does bilaterally mean on both sides right the chromosomes uncoil and you get cyto kinesis so you actually form this thing called the cleavage Furrow which is where the two cells are going to split you get the Reformation of the nuclear membrane these chromosomes that used to be like this so this is a cleavage frow that's going to form right here so you can see these sister chromatids that look like this are going to unwind again and become like that the cental the spindle Fiers broke down and the same thing happens on the other side and remember that now on either side of the cell you have this A and B and this A1 and B1 so do you see how this A and B is actually the same as what we had originally we have now successfully created two identical daughter cells to the beginning yay so exciting isn't that awesome isn't it cool how mitosis works even though it has nothing to do with toes and or sisters really annoying yo you get so many emails every time I come here you've got an email notification on your phone so let's go through that one more time and just take a look inside of the cells what's going on right as our good friend in the zoom chat asked us we'll go over the number the diploid and haid number for humans so humans start out with 46 arranged as 2N right so it's a pair and a pair and a pair all the way up until 2222 X Y I'm going to do my own right and then actually 22 is a bad thing because it's like it looks like 22 so let's say 17 17 18 18 dot dot dot XY right up until an XY is number 23 these are two 2 N single stranded 46 chromatids 2 N meaning double the actual number of chromosomes we have single stranded right okay when I have my S phase all of these become double stranded so it's one double stranded comma one double stranded right does that make sense and then it's two double stranded comma two double stranded so how many versions of my two number two chromatid do I have I have four there's two strands here and two strands here and that goes and goes and goes until X double stranded comma y double stranded and the X chromosome actually just looks like this and the Y chromosome just looks like this the Y chromosome is the smallest chromosome in the body because it contains the least amount of genetic information but what does it contain that completely changes the course of development what's the gene anyone there one gene that completely changes the course of development its activation changes everything now what it's called testosterone is the product right but I know what Gene it is it's called the sry Y Gene the sex determining region on the Y chromosome that's what sry y stands for now Excuse me while I put this Jolly Rancher in my mouth and for people watching on Zoom got it right and skep oh forgot to pick up my microphone back up skeptical as many people may be the religion of Islam actually talks about some of the effects of this Gene in a proper chronological order which was revealed over 1400 years ago you can read up on it this was actually uh the reason for a conversion of a very very very big geneticist in British Columbia Canada when he read what Islam has to say about embryonic development if it's not clear That's My Religion okay so that's mitosis that's how we make cells that look exactly like the parent cell what about meiosis what does meiosis do make sex cells right so now so we we talked about how that's how we keep the body going right cuz all of the cells in the body if it wasn't intuitive already because it wasn't intuitive to me when I was in college all the cells in the body body have all of the genetic material required to do anything they don't use all of it but all of them have it all cells in the body have all the genetic material required to do anything right but they don't just they don't use all of it it would it's a waste of time right so that's how we make cells within the body that are going to go on and make the heart and the skin the liver and the blah blah blah and whatever but how do we make cells that we're going to use to sexually reproduce right because we can make identical cells but like I said in the beginning if we have a cell like this where there's two of a specific chromosome and we want to remake a cell like this by combining two things we need to make a cell that is half of what it used to be and for a human that's going to be 1 through 23 double stranded so or sorry single stranded so this is going to be we're going to start out with two n 46 single stranded and we're going to end up with n 23 single stranded so when you look at a chromosome and it's single stranded like this and it this let's say this is the eighth chromosome this is the pair of the eth chromosome right when it replicates when it replicates we said that these two individual things on this specific version of the eth chromosome are called what sister chromatids do you guys know what these two things are called in reference to one another you ever heard of something known as a homologue these are homologous chromosomes these are homologous chromosomes right and they're going to become important when we talk about meiosis all right let's talk about meiosis meiosis actually has two steps and one of them is special so first let's Define meiosis generation of haid haid just meaning n cells for sexual reproduction split into two phases meiosis one and meiosis 2 meiosis 2 is mitosis so it's mitosis like meiosis one is the Troublemaker have you guys seen that um that reminded me have you guys seen that video on YouTube it's like really viral for some reason of that physics teacher who makes like really perfect straight dotted lines I think it has like 18 million views for some reason and he like angles his chalk a specific Direction and he like is able to bounce it up and down like that I just did it by a mistake but it's pretty cool you like have to apply like a certain amount of pressure and it just like allows the chalk to get the perfect amount of friction to bounce against the board and make a dotted line it looks like that if you know what I'm talking about if you're like as Niche and chronically online as I am then you you know what I'm saying and everyone's looking at me like I'm insane so there you go okay so let's talk about myosis one well let's talk about myosis in general right this happens it starts from the same place that mitosis does right so let's walk through it together so it starts from the post synthesis phase right after G2 where we have a such a shitty chromosome God this is why my parents don't love me no my parents love me very much starts off with 2 N double stranded or sorry 4N still confusing so for humans this is 96 H sorry 92 still confusing 92 thank you so it starts off as 92 in prophase one basically I'm drawing them as you would see them in prophase one because before that it's like loose it's not the nuclear envelope isn't open yet etc etc but in prophase one these things are going to meet up in the middle right these homologous chromosomes are going to meet up in the middle right so when they meet up in the middle they form this thing called a tet Trad right so that's basically like if you have something like this and then you have something like this it's going to combine with another one of these like in a 3D orientation that I can't show you where they're kind of going to line up on top of one another and that closeness basically like if they're like this they just line up like that like in 3D orientation they form a tetrad that closeness allows them to swap genetic information from the same domain of each of them why why is that interesting so let's say that we have a chromosome like this and we have a chromosome like this and this one's colored in right they're basically going to link up and they're going to say yo give me this and I'll give you or sorry wrong chromos chromatid give me this and I'll give you this so now this guy becomes empty and this guy becomes full do you see how that happens does that make sense why is that interesting cuz originally this guy came from a single chromatid right before all the synthesis phase happened and how did you get that single chromatid came from Mom right and how did you get that one it came from Dad right so now when Mom so this is the mom chromosome and this is the dad chromosome the homologous chromosomes and they swap information but now Mom has a little bit of Dad and Dad has a little bit of mom and that increases genetic variability and in order to get this to your mom the same thing happened between her mom and her dad and then to get it to them same thing happened between them and them so this is a way of increasing genetic variability across human beings right I look so much like my dad I look so much like my dad it's not even funny right but I have my mom's hair and I have my mom's eyes I have I have these I if you've ever seen me like face to face in person can hardly see my pupils my eyes are like the closest thing to Black you'll ever see right but my dad has these very light brown eyes I just didn't get them why get genetic variation you know and dominance and recessivity and this and that and a thousand other things that control genetics right there's no telling which is why like sometimes people are dumb and they're like oh well you know I have dark eyes and my spouse has blue eyes how the hell does my kid have blue eyes I thought this one wins over you can't tell there's like a million different things that play over here you you just never know right okay so this is how myosis begins and like I said meiosis one is the Troublemaker so what happened in mitosis after prophase metaphase they met up in the middle the spindles got thrown right so that's the same thing that's going to happen here but I'm going to show you I'm going to show you how they um how they differ so actually I'm going to leave this one completely colored in and I'm going to leave this one completely empty right so now they're going to meet up in the middle but crossing over is going to happen here this is called prophase but since we're in meiosis one this is called prophase one right then in metaphase one they've done their crossing over so you can see that little bit of influence that the other chromosome had on this and you can see the little bit of influence that that chromosome had on this and just imagine that these are stacked on top of one another right I might as well you guys get the picture hold on yes so these are both copies of the same chromosome correct they're lining up in the middle so I guess I could draw them side by side because they're actually not two different chromosomes so they meet in the middle after crossing over the spindle gets thrown but does anyone know the difference in what happen this is metaphase hey this is metaphase one does anyone know the difference in what happens during uh anaphase after in mitosis what did we separate we separated the sister chromatids here we're going to separate the homologous chromosomes right so this whole chromosome crossed over and everything and this whole chromosome crossed over and everything is going to migrate that way and that way so this is still 4N double stranded and I'm saying 4N as a total right the better terminology is 2 N double stranded equals 4N that's the correct terminology so this is still 92 and when anaphase and tase complete which happens the same way then say anase plus tilas is going to create two cells like this so this is going to have 46 but it's going to be N double stranded which is something we've never seen before in mitosis we've seen two N double stranded this is N double stranded a single chromosome without a homologous pair that has sister chromatids that's not seen in mitosis this is N double stranded which makes 46 2 N do you guys get the difference between this 2 N and this 2 n 2 N single stranded equals 2 N N double stranded equals 2 N and what is n for humans 23 46 2 N double 2 N single stranded is still 46 this is 46 with a homologous pair this is 46 without a homologous pair does that make sense Zoom chat everyone's dialed in right now or not doesn't make a difference to me I'm still teaching I said something last year that still holds true like if no one showed up there's like five six people in the room right now and this is always how it starts this is how it starts right it's always it started out with like four five six people and then December rolled around we got to like we got to like the peak of like orgo and bioen and you just saw like 10 15 20 I think one day we had like 30 people in the room and cuz people are scrambling scrambling to study for the MCAT that's what's going to happen um but we have a whole audience right here huh shout out to everyone on Zoom thank you guys for coming okay so now we have this N double stranded equals 46 chromosome and whatever happens to after this is mitosis it's just mitosis so what happens in prophase 2 this guy just either unfolds and then refolds and then nuclear membrane dissolves and whatever so it just meets itself in the middle right at metaphase so at metaphase 2 you've got this lonely guy crossed over at the party by himself so we're looking at this guy right here we're going to move forward with this one but know what happens to both right and then an so metaphase it's going to grab now it's going to grab the sister chromatids correct anase they're going to move apart and in taase you're going to get this and that do you guys see how those two come from a double stranded n chromosome so that means that this is n single stranded which is 23 and that's how we get back to 23 and then 23 + 23 is going to give us 46 yippee also I know I didn't explain all these secondary steps it's the same thing as mitosis just do it with out the homologous chromosome so in mitosis when the the homologous chromosomes both get their sister chromatids separated it's just that without the homologous chromosome understood okay that's cellular reproduction that's it I'm done talking about it speak now or forever hold your peace in what in meiosis before meiosis that even happens before mitosis so they're asking when did we make this 92 chromosome you come into meiosis with this right and when does that happen happens during the synthesis phase and the synthesis phase was before the G2 phase and it was after the G1 phase so it was within this thing we call interphase and the M phase is either mitosis or meosis so you come in with 92 chromosomes it doesn't happen within mitosis it happens before mitosis that's a good question I like good questions you guys ready to move on all right need your advice do we cut the YouTube video here and then move on with the reproduction or do we just continue on with the chapter it's up to you guys what do you think is more digestible cut it all right so that's cellular reproduction and then we'll talk about actual reproduction right after this be right back