 
S1: okay um, couple things i'm just trying to, tell you what's gonna, go on next week. keep you ahead um, you know that the exam is, coming up again the second exam on the twenty-first. please print out the exam that's in the coursepa- or on the uh, website. you should be able by now to probably do half of it at least okay? um, there's a huge, area of Meselson-Stahl's experiment, that was nonmultiple choice last semester that could help you um, and i think, if you get a head start on it you'll be better off. um, we're gonna be doing the, Sordaria lab on Tuesday. you will probably wanna read ahead, on that um, because he's not gonna be discussing that in lecture prior. and then you'll also have a five-point, assignment, i will probably give you something like, chromosomes are at two-N equals six please draw them in this stage this stage this stage etcetera. okay so that's, one more little five-point assignment that you'll be getting. Thursday you'll have another quiz okay? we wouldn't wanna let you uh, sleep or anything. and that will be over what he does next which, i believe is transcription and translation and will, also be over the Sordaria lab. and today, um we're gonna end with a quiz so you guys will have a chance to ask any questions that you might have and i'm ending with the quiz because, we're gonna do the chromosome dance which i think will help you, for the quiz, prior to that hopefully. but, uh before that, i wanna go over a couple things that you need, before, we actually, start the chromosome dance. and that, involves genetic recombination, and what does recombination mean? if i say, there's recombination, Meagan? 
S2: isn't that when the chromosomes overlap? 
S1: could be that's called what? 
SS: crossing over 
S1: okay, crossing over. and when does that occur? 
SS: meiosis. 
S1: which phase? 
SS: prophase. 
S1: prophase one. okay. so you could get crossing over and that would lead to recombination. can you think of another way you can get recombination? something that's not like the parent. 
S2: mutations? 
S1: okay mutation. but something naturally occurring with the chromosomes. 
S3: a mixture of the, paternal, per- paternal, genes. 
S1: okay, good. uh i just wanna illustrate that for you. i'll use the same alleles that we used, on Tuesday. <WRITING ON BOARD THROUGHOUT UTTERANCE> and let me just say, we've got dad here. and you had, A and B. okay? so i'll just say he's big-A, big-B... let's draw it small. and he mates with mom, who's little-A little-B. okay, these are unreplicated chromosomes or unduplicated. which means they're probably in G-one, they need to go through the S-phase. fertilization occurs. okay and they'll be brought together. and, it's just random, where they're gonna go, okay at this point. because they're unduplicated. okay? once they duplicate, if we're talking about meiosis what happens? okay if they're duplicated, what happens next? in prophase one? 
S4: pairing of the chromosomes. 
S1: mkay. homologous chromosomes are going to pair so, i'll just draw them paired okay? and this is just one option, of the way they could be paired. and what i'm trying to show you is that, genetic recombination can occur, through something called independent assortment. and that's just a fancy way of saying, random, alignment of chromosomes, at metaphase okay? and you should be able to follow this through. if this was, call it, metaphase one, picture anaphase one okay? and you get a cell, and telophase cytokinesis one you'd get a cell with big-A big-B. and you'd have another daughter cell with little-A little-B. if you can follow that through, post-meiosis two, <WRITING ON BOARD> okay you should realize that you get four daughter cells, okay that, one would have a big-A big-B, so would the other. and then you'd have two daughter cells that just had little-A little-B in 'em... this is after meiosis two, and, what do you notice about the way they look? these daughter cells. 
S5: hap- haploid appearance
S1: okay they're haploid. that was right. and they also look like, the parents, the original, parents. and we call these parentals, for obvious reasons okay. <WRITING ON BOARD> we just get, A B like dad, little-A little-B like mom. so these are called parentals... and there's been no recombination there okay? but equally likely, since this is just the nucleoplasm and these, things are floating around, you could've had, big-A assort with little-B. okay or vice versa. ahh so now post-meiosis two, you'd get something quite different, you'd have a cell with big-A little-B, <P :05> and little-A big-B... okay. and they look, different from the, parents okay? you could, assign any traits you wanted. but they don't look like either parent and for that reason they're called, recombinants. okay? so, you guys should understand the distinction first of all understand why this is random, okay? just random alignment in this fluid the nucleoplasm, that can't distinguish, who's lining up with who okay? if, independent assortment occurs, it's just as likely that you're gonna get, the same number of parentals as recombinants. okay? why, why do we want recombinants? why is that important? why do we care? 
SS: variation 
S1: okay, variation and that'll become important for evolution down the road. okay? okay. so that's independent assortment, understand that you can get, recombination through independent assortment. um, alternatively, we could show crossing over okay? and what that would look like, is let's say, you had a, reciprocal exchange between, the A gene on, chromatids two and three okay? what that would look like, would be something like this... Bs, were not involved so they stay the same. and you should be able to follow this through and see, why you wouldn't get, all parentals here. okay so after meiosis two just picture this, you'd end up with four daughter cells one with big-A big-B, little-A big-B, big-A little-B, and little-A little-B, okay. and this would be a parental type. these two would be, recombinants, and that would be a parental. okay. <P :07> if, crossing over occurs, it doesn't occur all the time, okay? and it h- so far we've just drawn one gene on a chromosome but there are hundreds. so you could picture a crossover at any locus, mkay? it may happen at one locus and not another. so with, crossing over you always get fewer recombinants than you do parentals. okay? with independent assortment it's a fifty-fifty, balance... okay, um any questions on that? this is gonna be real important next week when you start to do genetics problems. okay? <P :04> good? okay. uh, one last thing before we actually, fill in a table that we're gonna, go around the room and discuss. um, sometimes there're errors that occur in meiosis particularly meiosis one okay? and, those errors, may, happen, early, late metaphase. um more particularly anaphase one. okay, when, the chromosomes are supposed to separate, and maybe they don't okay? so if, there's an error, in meiosis, and i'll just put it in parentheses cuz it's most common in anaphase one... this is called nondisjunction and what it means, is the chromosomes don't separate properly okay? and, nondisjunction the reason i bring this up is because uh there's a table in your book we're gonna fill out next that, mentions nondisjunction. it's most common in meiosis one anaphase one and what that might look like, is let's just say, it's time for anaphase one to occur. you're used to, one A chromosome going, in one direction, the other, the other direction. let's just say, an error occurs. and both As, go to the left side of my cell, and no As go to the right. okay, so, i'd end up, with cells... after, telophase one, that were diploid for the A allele. <P :05> okay so this cell would be diploid for the A allele and you know that's, not what usually happens okay? and this cell would have no A allele. that's called nondisjunction, this cell would die, this cell this cell could persist imagine this being, haploid, okay, undergoing a second meiosis, maybe this is an egg. sperm fertilizes it, dad gives his copy of A, to the egg, and his copy of B, and now, you have a trisomy. mkay? um, you have three copies, of the A chromosome, and many times that's fatal. okay? uh in human situations that's how Down's syndrome comes about. we have three copies, of, the chromosome twenty-one. and those individuals tend to be fine. um, the other two chromosomes thirteen and eighteen that this, more, frequently happens to, those individuals tend, most of them will die before puberty mkay. so, this is nondisjunction, and typically it occurs, during meiosis one. mkay... okay. um before we do, the chromosome dance, in your coursepacks, there's a table <P :04> that, i'd like you to fill out. um we've already talked, quite extensively about the difference between mitosis meiosis one and meiosis two, now without looking, at your notes, and this should help pretty, extensively for the quiz too. just try to fill in the table. and we'll go around the room, and see how you did. yeah Bryant. 
S6: do you happen to have any copies of that? 
S1: no i'll go, i'll go get one though. cuz mine's, mine's filled in and that would be cheating. um, so try to fill these out. i'll go get you a copy and, we'll go around the room. and what i want_ how i want this to run is, let's say Joel says generates two diploid cells from a diploid. and he says meiosis one if that's wrong jump on him, okay and tell him why that's wrong okay? and, you guys, figure it out and let, each other know what's wrong versus me telling you. okay. so try that. i'll be right back. i don't' know if you wanna pause it or not. 
S1: somebody's in the lost and found. [S6: okay ] it's old though. 
<P :04> 
S6: so it's okay if i write on it? 
S1: yeah it's from last semester so i don't think they're gonna come back. 
SU-F: mhm 
S6: is it the same thing? [S1: hm? ] are there any differences? 
S1: no, no. 
S5: i don't have my book either. 
S1: you don't. <LAUGH> alright. <P :06> let me steal this for one second and make a copy. 
S7: you can make two.
<SS LAUGH> 
S1: this is discussion you guys you're supposed to have this. 
S6: somebody stole mine you have no excuse. [S8: i don't even know <LAUGH> ] someone stole mine you just left yours at home. 
S8: i don't even remember (xx)
S6: i don't care. you're supposed to be prepared for class each and every day. what happened to the (xx) alright. 
S8: i don't think it's that good because (i don't even them i don't even have a word.)
S1: okay who else...? actually just use this and you can just write in the book.
S8: thanks.
S1: that's just, cuz there're hardly any men in here. <SU-F LAUGH>
S1: you guys ready? [SU-F: yeah ] yeah? 
SS: yes 
S1: okay. how about if we start with Erin, and just go, around the room, read your question and then, say what you think. and if you think Erin's wrong or, anyone's wrong, um, tell 'em.
S8: i got a question real quick. can it be um, more than, [S1: yeah ] one [S1: yeah ] okay. 
S1: okay? 
S9: <READING> generates two diploid cells from a diploid cell. </READING> i put mitosis. and, after she asked that question i'm thinking, meiosis two, because it's the same as mitosis. 
S1: what do you start with though, in meiosis two? 
S9: haploid. 
S1: right. mkay so you, end with haploids too. so, just mitosis. everybody, agree on that? 
S5: mhm 
S1: okay so remember, you have to start out diploid in meiosis, but after meiosis one you have two daughter cells that're haploid already. mkay? those two daughter cells, undergo a further reduction division to produce four haploids. okay? 
S12: uh- <READING> generates two haploid cells from a diploid </READING> meiosis one. i don't, nope. 
S1: okay she sounds confident. <SS LAUGH> is that your final answer? 
SS: yeah 
S1: uh everybody agree? 
S4: no
S9: i put meiosis two.
S1: no? okay somebody thinks it's also meiosis two? 
SS: no
S4: no, (that creates) four. 
S1: okay Maria's right. um, you get two haploid cells from a diploid cell. why isn't it, meiosis two? 
S4: you get four 
S1: and what do you start with? 
S4: haploid. 
SS: haploid 
S1: okay you start with a haploid. remember, it's diploid at the beginning, then haploid haploid. mkay? so it's just meiosis one. 
S13: um, <READING> generates two haploid cells from a haploid cell. </READING> meiosis two. 
S1: mkay, everybody agree with that? 
S9: mitosis 
S3: mitosis. 
S1: okay mitosis. remember that haploids can undergo mitosis as well so don't forget that, you start out haploid you make two haploids. and, you have drawings, [S13: is it both or just ] sorry? 
S13: is it both of 'em or just mitosis? 
S1: uh both of them. mitosis and meiosis two... yep? 
S2: so like, how would, if by mitosis, which kind of cells like wouldn't be the diploid cuz you know how, like how could it be a diploid anyhow, for mitosis? 
S1: um, okay remember the, the drawings that i gave? let's just say_ i'll just use, two alleles. 
S2: well like for, uh um, prokaryote it would be like two haploid cells right? where, it just, the difference from like, 
S1: i- yeah it doesn't necessarily have to be prokaryotic, on fungus, there are many fungus that are haploid all their lives, like Sordaria is. but if you picture_ okay this is a haploid let's just say it has one chromosome, okay. and it can, go through, mitosis. <WRITING ON BOARD> and there's metaphase it's lined up, okay here's anaphase, mkay, and then telophase cytokineses would produce two haploids. [S2: mhm ] okay? so any ploidy can undergo mitosis. it's meiosis that you need the homologous, pairing on multiple of two. 
S9: is that for one and two? 
S1: sorry? 
S9: is that for one and two, just haploid, for meiosis one and two? 
S1: um well thi- this was, wait where are we here? two haploids from a haploid. so that's mitosis and meiosis two. okay? okay. 
S5: <READING> homologous chromosomes separate during anaphase, </READING> i put meiosis two. 
S1: anybody agree, disagree? 
S4: disagree 
SS: disagree 
S1: disagree why? 
SS: meiosis one. 
S1: okay meiosis one. you don't have homologous chromosomes at meiosis two anymore remember because the homologues have separated out, and meiosis two is similar to mitosis. mkay? so the, homologues don't pair anymore. so it's just meiosis one. 
<P :05> 
S2: um, <READING> sister chromatids separate during anaphase </READING> meiosis two. 
S1: okay anybody wanna add anything to that? 
SS: mitosis 
S1: mitosis. okay. so remember sister chromatids will g- separate, during anaphase. they won't, during meiosis one anaphase one, okay? but they do, in meiosis two anaphase two. 
S14: okay um, <READING> sister chromatids are not necessarily identical </READING> um, i put meiosis, one? and two? 
S1: and why might they not be identical? 
S14: um cuz they might have different alleles. 
S1: from how? 
S14: crossing over 
S1: mkay. good. everybody agree with that? meiosis one and meiosis two you might have, nonidentical, Katrina? 
S5: when does crossing over occur? 
S1: prophase one meiosis one. mkay? 
S8: <READING> sister chromatids are identical. </READING> uh mitosis and meiosis one.
S1: uh, um yeah they they could be iden- if no crossing over occurs sure, they could be identical i- i mean, i- actually it could be all three, as long as no crossing over no recombination occurs. but you know they're identical, absolutely in mitosis for sure. okay there's never any crossing over in mitosis. [S8: okay. ] so that's, that's kind of an arbitrary. okay. 
S15: um, <READING> D-N-A replicates prior to prophase. </READING> i put mitosis and meiosis one. 
S1: mkay. everybody agree with that? that you have, replication the S-phase prior to mitosis and meiosis one. 
S13: no. why's this? why isn't it in mitosis, i mean (meiosis two?)
S1: why what? why not be be, okay think of what you end up with after meiosis, one. you end up with, haploids. <WRITING ON BOARD> but they're duplicated already right? they're still duplicated because the centromere has not divided. [SU-F: mitosis and meiosis one ] mkay so, they wouldn't duplicate again. you're trying to reduce the amount of genetic information, during meiosis two. okay and that is what happens. 
S13: so, the answer is, mitosis and meiosis one? 
S1: right. 
<P :05> 
S6: oh okay uh, <READING> D-N-A does not replicate prior to, prophase. </READING> i just have meiosis two. 
S1: mkay. is there anybody, disagree? wants to admit it? no? okay.
S4: <READING> crossing over, can occur </READING> i put meiosis one and two. actually, 
S1: wanna take something back? 
S4: um, not meiosis two. 
S1: mkay, yeah just meiosis one. why can't it occur, during meiosis two? 
S11: cuz they don't have homologous chromosomes. 
S1: right, there's only one copy they're haploid then there's no ho- homologue to, pair with and cross with okay. 
S11: <READING>nondisjunction can occur, </READING> i put um meiosis one. 
S1: okay. nobody would disagree with that right since you just learned about nondisjunction, <LAUGH> a moot point 
S16: uh <READING> centromeres divide, </READING> i put, mitosis, and i think, does that happen in meiosis two? [S1: yeah ] that's what i put [S1: yeah ] but i wasn't sure. 
S1: does everybody like that? 
S6: centromeres don't (divide?) 
S1: no, centromeres don't divide remember? why don't they? 
S5: cuz isn't it the whole chromosome though? 
S1: why? 
S9: spindle attached to the wrong side. 
S1: right, the spindle fiber's only attached on one side of the chromosome, whoever, asked that, so they can't it just pulls, one chromosome that way and one, the other way. unless, nondisjunction occurs okay? 
S17: <READING> individual chromosomes align at equatorial plate during metaphase. </READING> um i said mitosis and meiosis two. 
S1: okay. both with mitosis and meiosis one because they're l- i'm sorry two because they're lining up, single file. 
S18: um, <READING> homologous pairs of chromosomes align, at the equatorial plate during metaphase, </READING> meiosis one. 
S1: okay. everybody agree with that? 
SU-F: mhm 
S1: Rebecca. 
S19: <READING> um occurs in sematic cells </READING> uh, mitosis? 
S1: mkay sematic cells is mitosis. so, sex cells whoa. 
S20: <READING> occurs in sex cells, </READING> meiosis one and meiosis two. 
S1: mkay, meiosis one and two, are for sex cells.
S10: <READING> produces two daughter cells that are genen- genetically identical, to each other and to, the parent, cell. </READING> mitosis and meiosis two. 
S1: and what? 
S10: meiosis two. 
S1: we're talking the, the very original parent. [S21: (mhm) ] so, how does the original parent start out? in meiosis? what's its ploidy? 
S10: meiosis is, haploid. right? <LAUGH> (xx) 
S1: anyone wanna help her out? meiosis has to start out diploid why? 
SU-F: mm so it can breed and cover one another
SU-F: because it can't replicate within meiosis.
S1: right you have to have a homologous pair, okay? so you have to have two of each, so you have to at least have some, i don't know some, uh multiple, of two. so, i'm just trying to get to the final answer, why, why it's not meiosis two. if it starts out diploid what're your four products of meiosis? what's the pro- the ploidy of your four, end products of meiosis two. 
SS: they're haploid 
S1: they're haploid right. so can they be identical to the, original parent? no. they have half the genetic 
S10: i thought that they meant the original original. like the 
S1: they do, and the original original, is diploid. [S10: okay ] and and so the, progeny of the gametes have half the genetic information as the, as the parent. 
S21: um, <READING> produces two daughter cells, that're not genetically identical to each other and to the parent cell. </READING> meiosis one and meiosis two. 
S1: mkay? everybody agree? okay. i think it 
S5: do cells either have to like, go through mitosis or meiosis one and two? 
S1: yeah, if you're a germ cell and you're gonna become a sex cell, you undergo meiosis. mkay, if you're another type of cell in the body you undergo mitosis. 
S5: right so they never go through, like all three.
S1: um actually germ cells do. li- okay picture this. a sperm and an egg, come together fertilization occurs, you have a single, diploid zygote okay it's a single cell, it's diploid. somehow you have to, grow into a multi-cellular being, that includes the germ cells. so mitosis occurs in each of, you know skin cells nerve cells germ cells. and the germ cells s- starts out diploid. okay? and then when it's going to become a sperm or an egg, it goes through meiosis. but the germ cell's the only one that will go through both. okay we don't wanna leave you guys out. um, Katrina, why is it important to, [S10: oh my, ] ensure constancy in meio- mitosis m- mitosis, produces constant, cell line, identical cells why would that be important? 
<P :04> 
S5: i don't understand the question. 
S1: um, it's right there, the crucial difference between mitosis and meiosis, is encapsulated by the statement mitosis is a mechanism for constancy okay? so, if you have a liver cell, why is it important to make more, liver cells? why do you want, identical, an identical clone of cells? 
<P :04> 
S5: um <P :05> because if it's the, liver cell you want more, uh, you wouldn't want, it to be like... i don't know. 
S1: anyone wanna help? constancy? 
SU-F: for the purpose of regeneration like for instance with your skin.
S1: okay. Bridget's saying for regeneration obviously if you want a skin cell you want that same clone of skin cells you, you don't want it mutated so it's an abnormal skin cell. um you don't want a liver cell growing in place of it so you wanna turn genes on, that're going to express liver, proteins or whatever to make a liver cell, and turn those off that don't mkay? versus, Rasheda, why would you want, diversity in meiosis? why is diversity so important? 
S22: for when you go, later on down, with it n- the gene- uh, it'll become, it'll be more important later on down the, [S3: evolution ] to, <LAUGH> 
S1: okay, so, for evolutionary purposes right. if everything was the same, there'd be nothing for natural selection to act on, okay? um, and we're gonna, start getting into, natural selection, pretty soon, pretty much after exam number two mkay? okay Joel. does chance play a role in either mitosis or meiosis? 
S3: meiosis. 
S1: mkay. and, how? how is there chance? 
S3: recombination, crossing over nondisjunction. 
S1: mkay? crossing over nondisjunction or just independent assortment. just the random role of about lining up chromosomes mkay during, metaphase. okay, um this is a real good test for you guys to take again and, like right before the exam, it should_ if you can just answer these questions cold and don't have to, to look up in your notes, you should be pretty well prepared for the exam as long a- as you can draw things, mkay? um, okay, hopefully this will help with the quiz as well this little chromosome dance simulation. um, basically this is set up to illustrate, human chromosomes. you guys are gonna be human chromosomes we're gonna start with four unreplicated, human chromosomes, and then, you're gonna duplicate yourselves, mkay? and, i've got some alleles here. being sort of sex biased, i have big-B, being bad breath little-B being fresh. big-C being crabby, little-C being cheerful. and, i don't need four, men with bad breath, that're crabby. but, my, male, sperm, is going to carry an allele for bad breath, and a and a separate allele, for the crabby gene mkay? notice that these are unduplicated chromosomes at the time. and also notice, that, fertilization's going to occur, you guys should be able to take these chromosomes through, both mitosis and meiosis and understand what happens so it's going to be up to the, individual alleles to move the way you should. and the rest of you watch the way they're moving, and if they're doing something wrong let 'em know. mkay. alright. um, throughout_ first we're gonna do mitosis which is, is pretty easy, and then we'll, go to meiosis so, what i need, is four volunteers i need, bad breath, mkay who wants to, be the bad breath allele? <SS LAUGH> don't all stand at once right? bad breath and crabby i need one of each. c'mon... okay, Erin? which do you prefer? 
S9: crabby, 
S1: okay stand up please. okay the hands are gonna represent, chromatids and, these sticky notes don't stick too well but, here's her crabby allele, okay. whose got bad breath? besides me because i had onions for lunch. okay... bad breath. uh who wants to be cheerful? nobody? [SU-M: man ] <SS LAUGH> and, cheerful? 
S4: i will be, 
S1: okay. Leslie's cheerful. i can feel it. um, fresh breath, 
S5: (i can't believe we're doing this.) 
S1: okay Meagan. <P :04> okay. these guys are, unreplicated. meaning they're each double stranded D-N-A molecules, but, they're unreplicated. when you become replicated, your elbows are gonna be the centromeres, so whoever's gonna be your partner, i can see that, participation is, great, um, these, you're gonna join in the centromere okay? so keep that in mind this is our centromere, and this is the rest of our chromatids. okay, so i need the parentals to be together, let's see so you guys just kinda step over there. you're the sperm, you're the eggs. <SU-F LAUGH> okay, come together, fertilize. okay you're all together in a cell, [SU-F: wait, wait ] and you're still all unduplicated. mkay you're all doing well. um, now we need, four more volunteers, to replicate who wants to replicate with Meagan? fresh breath. <SS LAUGH> <P :05> she's getting a complex who wants Meagan...? 
SS: come on 
S11: Nana says she will. 
S1: Nana will. <SS LAUGH>
S1: those of you that don't volunteer now get to do meiosis and it's much harder, okay? uh bad breath. [SU-F: so that's alright. ] okay Morgan. 
S6: e- everybody alright. <LAUGH>
<P :06> 
S1: okay i need a crabby and a cheerful. okay Rebecca. <P :09> okay. so, are you replicated? join at your centromeres please. 
<P :04> 
S19: does it matter if we're, against the wall? 
S1: it doesn't matter. just as long as you can see the, they can see the signs. okay what's going on in prophase of mitosis? anybody. four things. 
S10: random. 
S1: okay it's random, what else...? 
S10: chromosomes (xx) 
S1: well that that's, that's 
S6: um, the chromosomes are condensing. 
S1: okay they're condensed. you can see 'em, you can see 'em, you can see 'em under the scope. okay what else? 
S8: um, spindle fibers form. 
S1: spindle fibers form. okay. uh what else? 
S5: centromeres go to the opposite sides of the cell. 
S1: centrosomes [S5: centrosomes ] go to opposite side of the poles. 
S5: nuclear envelope disappears. 
S1: nuclear envelope disappears. okay. are you guys just at random in the nucleoplasm? or are you paired? are you just there? 
SS: random
SU-F: we're just, there. 
S1: okay you're just there. okay these are the prophase chromosomes. alright, let's get into metaphase... okay are they right? is that right? [SU-M: uh'uh ] okay they're lined up single file and something to notice is that they would have spindle fibers on each side of them, okay? anaphase one. not one just anaphase. <P :04> <SS LAUGH> nondisjunction in mitosis. okay, good. um so this is anaphase, now telophase is going, going to occur, followed by cytokinesis. you guys are now two daughter cells, your job is pretty much done. show your alleles to everybody. what do you notice about these, two daughter cells? 
S11: they're haploid (in appearance?) 
S13: it's the same as the parents.
SS: identical 
SU-F: they're identical to each other and the parent. 
S1: right. you guys are not only identical to each other, you're identical to the original parent. what's your ploidy? 
SS: diploid. two-N
S1: two-N equals, [SS: four ] four. okay. thank you very much. that was wonderful. okay. 
S13: you want these? 
S1: yeah. these are for my next, batch of volunteers. okay, meiotic chromosomes same thing, i need <P :06> i need, four people. and i'll just hand you thi- alright somebody, Loretta, <SS LAUGH> i'm grabbing you now. you're bad breath just for that. okay. Alicia, you're fresh breath. Jerry you were up, were you up? 
S18: nope. <SS LAUGH>
S6: that girl don't know nothing. 
S1: okay. we need four more. and i have these... okay. this is meiosis. so sperm separate from the egg please. <P :05> okay, fertilize if you will. <SS LAUGH> okay, so, now_ they're not replicated yet, fertilization has occurred. now we need four more people. 
S6: go ahead, no that's alright 
<P :04> 
S1: crabby, now who else am i missing? <P :04> i didn't think so, you're just hiding on me. okay... okay join at the centromeres. find your partner. 
<P :10> 
S5: Laury, is this the part where the, the chromosomes are replicating themselves, when they find a partner? (xx) 
S6: this is where they're condensing 
S1: um, wh- when i say partner wha- what's going on now is, semi-conservative replication where, the helicase comes in unwinds brings in all that stuff, brings in the bases. when, when the homologous chromosomes find a partner, that's when like chromosomes pair. so there will be_ watch this okay. alright, we're in prophase one now. so what should be going on? 
S6: condensing, 
SS: condensing
S1: you're condensed. [SS: spindles ] spindles, your centrosomes are out here. [S6: nuclear envelope is gone now ] um, nuclear envelope's gone, what else? 
SU-F: oh homa- homologous, chromosomes pair 
S1: okay homologous chromosomes pair so do it. it's up to you to figure out who's homologous... what does homologous mean? 
SS: the same. 
S1: carrying the same genes right? so i have the breath gene, whether it's bad or good. and have i- the mood gene whether it's bad or good those are homologues. okay so cheerful is paired with crabby, fresh is paired with bad, okay? now, typically you guys are so close together, that there's h- you can't even distinguish between, the four of you. i won't make you do that yet. <SS LAUGH> um, okay. so, prophase one, you're paired. get into metaphase one please. <P :08> <SS LAUGH> okay, is this good? [SS: yes. ] very good okay, the homologous pairs have lined up, where are my spindle fibers? there would be a spindle fiber here on Natasha's arm, and here on Naomi's arm. and poor Felicia and Loretta have no spindle fibers so therefore, they can't_ they're just very close together. and they're not gonna be pulled apart, from their partner ultimately. 
S8: i got a question. 
S1: okay. mhm
S8: she wouldn't have a spindle fiber, just 
S1: oh Bridget does too. yeah i was just using the front row. yeah Bridget would have one, and Joel would have one but in between poor Jerry, Bryant no. okay. okay so anaphase one. okay, since these four had no spindle fiber, 
S7: are we staying? i mean i'll stay but you know 
SU-F: in the middle don't they stay? 
SS: no 
S6: no they stayed but don't they 
S1: no you you guys are going [S6: oh okay ] to opposite poles okay. but you can't detach because you had, the four of you, had no spindle fiber that's very sad so you have to go with your, your neighbor okay. 
S6: and that's because of the, what's that? [S3: spindle fiber, ] like, i can't even remember what the thing is called. [S1: spindle fiber? ] no co- 
S3: kinetochore. 
S6: no kinetochore.
S1: oh you, you have a kinetochore. 
S6: but, it's on his side though. 
S1: no your kinetochore is here. it's it's over here 
S6: so, it's still it's still going through like my side too. like it's going through, like the spindle fiber is not, staying in his side it's like going all the way through. 
S1: it it can't it's, just staying on his side yeah cuz you guys were so close together that there's no room for it to get in there. 
S6: but the centromeres haven't dissolved yet. is is that what it is? [S1: right ] okay [S1: right. ] 
S1: centromeres haven't divided [S6: okay ] that's why you're still attached. 
S5: so like the centromeres are even attached to the kinetochores on, each chromosome [S1: right ] it's just the proteins right? 
S1: right. yep. everybody has a kinetochore. that's not the problem, okay the problem is the spindle fiber attachment. okay, so, meiosis one would occur, be over. telophase, one cytokinesis one and you'd end up with two daughter cells. how do they look? those daughter cells? what alleles do you guys have? 
S6: identical to their parents. 
S1: oh you guys ended up identical but it didn't have to be that way did it? 
SS: uh'uh, no 
S1: no cuz Brian and Joel could've been over here, Jerry and Bridget could've been over there and then they would look, recombinant right? what's their ploidy? 
S6: two-Ns
SS: two-N 
SU-F: four-N equals eight 
S1: ahh. 
SS: no, two-N 
S4: what is_ whose, ploidy? this whole cell like this? 
S1: this whole cell and this whole cell. 
SS: two-N equals four.
S3: two, one-N
S4: is that one-N equals two?
S1: how many, mood genes, mood, chromosomes do you have? 
SS: one 
S1: how many, breath chromosomes do you have? 
S4: oh i keep thinking it's_ oh i know what you're talking about now.
S5: so one-N equals two? 
S1: one-N equals two. and that's because the centromere didn't divide, [S4: yeah i forget. ] these are still duplicated to chromosomes okay? so don't forget that you start out diploid after meiosis one, you're two haploids, mkay? now you guys need to go through, meiosis two. and so get in, prophase two. uh you are okay. metaphase two... anaphase two. [SU-F: separate ] okay. cytokinesis telophase two. now we have four daughter cells, that look how? 
SU-F: different? 
S1: different, because they have half the genetic information as the original unreplicated parent, and it just so happens that they all lined up together so we don't really have any, recombinants per se here but we could've because it's random, okay? now if you'll just get back together with your, homologue one more time i'm just wanna show, crossing over. get back where, metaphase one. okay now i want just Jerry and Bryant, to cross over so just, swap tags. yeah or swap sides whichever you wanna do. 
S6: what're you gonna do man?
S7: God, it's not that hard. 
S1: okay, um, anaphase one... okay, cytokinesis you're, haploid. okay, now just go through meiosis two show me, the end products of meiosis two. okay good. now Natasha and Joel have bad breath and they're crabby. mkay. that looked just like dad, right? mkay, um, Loretta has bad breath, but Bryant's cheerful. is that parental or, recombinant?
SS: recombinant.
S1: okay that's recombinant, mkay? Felicia has, fresh breath, Jerry's crabby, parental or recombinant? 
SS: recombinant. 
S1: recombinant. and then Bridget's, cheerful, and, Naomi's got fresh breath so, those were parental. okay? i think you can visualize what would happen with nondisjunction. okay? if you'll all get back together one more time with your homologues. okay, nondisjunction, we're gonna have, Brian and Jerry separate but we're gonna have Felicia and Naomi come over here. okay? okay. so now, poor, Jerry and Bridget are gonna die because they are gonna be <SS LAUGH> in a cell, with just one chromosome and they're missing the entire, second chromosome that they need with all the proteins. okay? 
S3: but we have Down's syndrome <SS LAUGH>
S1: but that's okay. um, so these guys, fertilization's going to occur, right? we'll just call you an egg, fertilization's going to occur. and now i have, bad breath. okay? so there's three of us, and my homologue does too. now we have three, alleles for bad breath, and, therefore it's called a trisomy for three. and, that's not too devastating we just go with, bad breath for the rest of our lives okay? but that's nondisjunction where somebody ends up with none. okay and somebody ends up with, one. 
SU-F: does it matter that he's still um, i mean, like had a crossover? 
S1: no. no that's fine. you can have, you know nondisjunction with crossing over, whatever. okay thank you chromosomes you did an excellent job so, hopefully try to visualize that cuz you guys seem to know what you're doing. and if you can visualize what's supposed to be happening that's sometimes helpful for, the exam. but first for the quiz, okay? you know what's on it. there's all the uh, cricket lab, cricket lab's on it um, D-N-A replication Meselson-Stahl the experiments where she chased Avery-Griffith mitosis meiosis. 
S2: um, what's the ploidy af- after meiosis, one? 
S1: what's what? 
S2: the, ploidy after meiosis one? 
S1: okay after meiosis one, what is the ploidy? 
SU-F: one-N equals, 
SU-M: eight 
SU-F: one-N equals thirty 
S1: okay... uh the question is what's the ploidy after meiosis one? 
SS: one-N equals two. 
S1: one-N could've equal any, one-N could equal ten. [SU-F: oh okay. ] okay? um, sperm cells one-N equals twenty-three in humans. okay there're twenty-three different chromosomes in the sperm but there's only one copy of each, okay? so, you started out with forty-six, and after meiosis one, you have two daughter cells that each have twenty-three, different chromosomes. 
S3: how many genes are on one, chromosome? 
S1: typically about a hundred. mkay and that's sort of a ball, hundred hundred and fifty, that's kind of a ball park, figure for how many genes are on chromosome. yeah and, and one thing we've done is we've just done unlinked genes, but keep in mind you could have A-B-C-D, that're all linked, and crossing could occur at any point, on the, chromatids. so, you may see crossing over with respect to one locus but not the other, twenty-three. mkay. 
S5: so then N represents the copy of each, chromatid? 
S1: chromosome. 
S5: chromosome. 
S1: yeah. don't even use chromatids in this class cuz it'll, confuse you i think more than anything. just know, this a, chromosome, that's unreplicated, this is a chromosome, that is replicated. 
S5: okay. 
S1: okay. Meagan? 
S2: so when we're doing the, the diploid, then, or like just whatever the ploidy, you go by the letters like, so if it's A and A, even whether they're large or small then that's considered like, one kind. [S1: right. ] and that so then like, if you have say you have one chromosome, with a big-A and another one, with a little-A but they're not like, replicated then you would say two, two-N? [S1: mhm ] but what if it's replicated and you'd be like, a replicated one with As and a replicated with little-As. 
S1: then it's still two-N. 
S2: it's still two-N? 
S1: yeah okay what's the ploidy of this cell? 
SS: three-N equals
S1: i knew you'd say that. [SU-F: it's wrong? ] it's just two-N right? there's two of each kind of chromosome. sure there's three different kinds, [SU-F: oh ] okay? but there's two of each. okay so don't, get that confused. this would be two-N equals what? 
SS: six 
S1: six okay? so, ploidy, the N, means, number, of different, chromosomes. if there's one of each, different chromosome, it would be haploid. okay? if there's two of each, different, chromosomes it would be diploid. triploid i'd have to have three of each. and you don't wanna see that. that only happens in plants. usually, and, they live to tell about it. mkay... mkay? Natasha? 
S18: what's important about the crickets lab? 
S1: oh, well you should be able to put any of the, substrates with any of the enzymes and tell me what would happen. <SS LAUGH>
S10: Laury, it's just like i can't remember exactly what those substrates did. 
S18: i can't even remember their names. 
S1: that was the first exam you can get, 
S1: <WRITING ON BOARD> okay, glucose is a substrate for what? 
SS: glycolysis. 
S1: glycolysis. in order for glycolysis to happen, where does it happen what do you need? 
SS: cytosols 
S1: cytosol. so if i put, glucose with whole homogenate. could glycolysis happen? 
SS: yes. 
S1: <WRITING ON BOARD> could respiration? 
SS: yes. 
S10: oh, i remember that. 
S1: does everybody understand why both those processes could occur? 
SS: yes. 
S1: did anybody say no? okay? okay. glucose, <WRITING ON BOARD> plus supernatant. could glycolysis occur? 
SS: yes 
S1: why? 
SS: because the cytosol 
S1: okay. so glycolysis occur could respiration? 
SS: no. 
S1: why not? 
SS: no mitochondria
S1: no mitochondria. okay. you know this. <WRITING ON BOARD> glucose plus pellet can glycolysis occur? 
SS: no. 
S1: why not? 
SS: no cytosol. 
S1: no cytosol. could respiration? 
SS: yes, no 
S1: no? why? 
S5: because don't you have to (go through) glycolysis before you can go to respiration? 
S1: yeah, yeah. if you don't have pyruvate, or succinate which is a pyruvate substitute then you can't go through respiration so this tube could do nothing. <WRITING ON BOARD> okay and the only other thing you have to worry about is succinate, succinate plus whole homogenate, any glycolysis? 
SS: no. 
S1: why? 
SS: because there's no glucose 
S1: no glucose, any respiration? 
SS: yes. 
S1: okay. okay succinate, plus supernatant. glycolysis? 
SU-F: yes, 
SS: no. 
S1: why not? 
S5: cuz there's still no glucose right? 
S1: no glucose, respiration? 
SS: no
SU-F: no, no mitochondria. 
S1: no mitochondria, okay so, nothing there. and lastly, succinate, plus pellet. glycolysis? 
SS: no
S1: no. respiration? 
SS: yes. 
S1: yes. <WRITING ON BOARD> okay. so if you can keep that straight, i think you're, 
S5: you said pyruvate is a, glucose, substitute? 
S1: pyruvate. wait i'm sorry? 
S5: what is pyruvate, a substitute for? 
S1: succinate, is a pyruvate substitute. [S5: okay. ] okay? glucose is broken down into pyruvate, which feeds directly into the Krebs cycle for respiration. okay? s- but you could substitute anything in the Krebs cycle for pyruvate, and it would work. okay? good? 
S5: mhm. 
<P :07> 
S1: alright? you're good with everything you're ready, bring it on, 
SS: no
SU-F: no, the experiments 
S11: oh no.
<S1 LAUGH> 
SU-F: i told you.
S11: let's have a summary of all of 'em. 
SU-F: no 
<P :05> 
S1: okay, um, experiments, anything specific?
S4: Griffith's was the S-cells and the R-cells. 
S1: okay [S11: that's the rats? ] you inject the mouse hm? 
S11: the rats right? [S1: yeah ] mouse whatever. 
S1: you inject the mouse with [SS: S-cells ] S what happens? 
SS: they die
S1: why?
SU-F: cuz they had pathogenic
SU-F: they had a capsule around it
S1: mkay. cont- contracts pneumonia and dies. [SU-F: basically. ] okay? mouse plus R-cell does it have a capsule? 
SS: no. 
S1: no. is it virulent does it cause pneumonia? 
SS: no 
S1: no. does the mouse die with it? 
SS: no, 
S1: no. heat killed S. what's heat killing do to the S-stain? 
SS: breaks up the capsules 
S1: breaks open the cap- breaks up the capsule basically destroys the cell wall so it's just naked D-N-A, in solution. and what happens to the mouse? 
SU-F: it lives. 
S1: okay it lives nothing's wrong with it. so alone, live R didn't kill the mouse. alone, heat-killed S doesn't kill the mouse, why does a combination of the two kill the mouse? 
SS: cuz transformation 
S1: okay transformation occurs and what di- what's being transformed to what? 
SS: the S and R 
SU-F: R is transferring to S
S1: mkay, so, basically, something from the S is getting into R, transforming it to becoming S, and killing the mouse. did they conclude anything more than that? 
SS: no. 
S1: no. okay? and then it took Avery, what'd Avery do? to a purified solution? 
SU-F: he took the chemicals from that and made them 
S5: killed the mouse and killed the D-N-A
S1: okay you take D-N-ase, mkay that kills D-N-A. and if D-N-ase wipes out the D-N-A do you see transformation occurring? 
SS: no
S1: no. what about protease that kills the protein? 
SU-F: it still transforms 
S1: mkay. still transforms, and therefore what did, Avery conclude? 
SU-F: the D-N-A was the uh, 
SS: transforming agent 
S1: mkay, D-N-A is the transforming principle and not protein. and, protein's so much more complex. there're twenty amino acids there're various ways, millions of ways to hook 'em up. so it was disputed, pretty heavily, debated that uh, D-N-A which is much more simple could be, that important for the genetic material. okay. okay? <P :04> good? okay, do you guys need to? ther- it's quiz time so if yo- 
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