Humans have 23 pairs of chromosomes for a total of 46. A 23 of those chromosomes come from your maternal mom side of your family and your other 23. Come from the paternal side or your father think about why our cells would want to organize our dna into chromosomes in a moment. We’Re going to understand that the dna is duplicated and then split into opposite sides of what will become two cells, and so that would be really difficult to do because dna, if it wasn’t structured into chromosomes it’s a macromolecule there’s a lot of it. So it’d be pretty difficult to account for all of it, so our body has a way that we can organize that really long strand of dna. All of all of our dna into these structures by wrapping the dna around histones, forming chromatin and then coiling that chromatin into chromosomes here’s, the parts of the chromosome chromosomes actually made up of two chromatids, so either side of this chromosome. This is one chromatid. This is the other chromatid, together, they’re sister, chromatids and they’re joined near the center in a structure of protein called the centromere that attaches those two chromatids together, your chromosomes are homologous. You heard me say earlier that you get all 46 of your chromosomes from your parents. 23 from mom 23 from your dad, so they’re homologous, meaning that they’re the same well. All of the genes are in the same place compared to your mom and dad’s chromosomes.

They gave you it’s just that the genes might be different in that one might be dominant. One might be recessive, so they’re the same genes different in how all of those nucleotides that make up those genes might be slightly out of slightly different due to mutations and other events that increase genetic variability. Take a look at this karyotype. It carry types, an image that shows an individual’s chromosomes arranged in homologous pairs based on size order. So these are, if you count them all up, 46 chromosomes and geneticists might want to make a karyotype like this, because i can help them determine potential conditions. For example, if an individual has an extra third, 21 chromosome or chromosome number 21, if there’s a third of them, a third of the of them here, then the individual would have down syndrome. Take a look. 22 of these pairs are called autosomes and then one pair determines our gender. These are called the sex chromosomes. The one listed here on our screen is x y, which is typified by a biologically male individual x x. If you have two x chromosomes, then you’d be biologically female chromosomes, uh chromo means color, some means body, and so it literally means colorful body. That name came from this uh. The staining process or the dyeing process will be attractive to certain stretches of dna and it creates these colorful band patterns that the geneticist uses to match up those homologous chromosomes and they are kind of colorful aren’t.

They so take a look here. This is the cell cycle, all parts of it, including interphase, mitosis and cytokinesis, recall that in interphase there’s, actually, three substages to it g1 s and g2, g1 or gap. One in interphase is the the time of the cell, where it’s doing its normal functions, it’s uh doing the central dogma of biology, which is dna to rna and making protein from it. G1 is when the cells are living to its highest biotic potential. Um, hey, there might be a signal from outside the cell to begin replication, and so the cell would move from g1 into s. Phase of interphase s phase is well. S stands for synthesize and that’s. The moment when the dna is duplicated, we replicate an exact copy because think about it. That one cell is eventually going to become two and both cells need to have an exact copy of the dna. Otherwise it will be able to live to its highest biotic potential. So if everything gets synthesized properly, the cell will move into gap 2 or g2 of interphase preparation for mitosis, and it starts with prophase lots of stuff happens during prophase. The nuclear membrane begins to break down here. Hey those centrosomes with their centrioles, begin to move to opposite sides of the cell, recall that the centrosome is where the spindle fibers radiate out from they’ll, eventually attach to the centromeres of the chromosomes. As that nuclear membrane breaks down, the chromosomes also start to form.

So the chromatin begins to organize itself into these structures. Here. Take a look here. This is what it looks like in plant cells. Look at the difference, uh notice that the the dna or genetic material is kind of in the same general shape right, because that nucleus is present in interphase and it begins to start to break down in prophase. So the dna is more or less contained within that area of where either the nucleus is or where it’s kind of still is as it’s dissolving away, but notice too, that the dna starts to uh condense here right. That chromatin is going to organize itself into chromosomes and that’s. Really the big takeaway here from or the big giveaway that you’re looking at prophase versus interphase is those dark structures that you can start to see the the chromosomes start to form up uh all right. So if everything checks out, the cell will move from prophase into metaphase. Those spindle fibers that are attached to the centrosomes on either side of the cell will begin to push and pull those chromosomes into the center. The pushing and the pulling kind of averages out so that the chromosomes line up along what’s called the metaphase plate in the center or the equator of the cell, and this is what it looks like here in this uh in a plant cell right here. Right all. Those chromosomes uh lined up along the middle because after metaphase comes anaphase that’s when those chromatids move to opposite sides of the cell, so the spindle fibers pull the chromatids apart, and this is what it looks like in the cell here right.

Those purple structures are the chromatids being moved to either side of the cell. At the end of anaphase, the cell will move into telophase and cytokinesis telophase. It looks like this here in the plant uh in a plant cell, so notice that looks like the the dna is now unwinding. That chromatin is a little bit denser, and so you can kind of see an indication of some chromatids. But you can imagine that that dna is starting to unwind. The nuclear membrane begins to form anew and uh. Motor proteins are going to help pinch off, create a cleavage furrow and pinch off the cell as it moves and creates. You know two cells from the original one. Now it looks a little different here in plant cells uh. Why? Because plant cells have a cell wall, a rigid cell wall and so that pinching off process can’t really happen the same way it would in an animal cell, and so what plant cells do is it starts to build up a uh, a cell wall that will cleave The cytoplasm into two sides so uh take a look here. Another photo let’s go through each one of them again. Here’S interphase notice that this picture, the dna is kind of ghosted uh. These dots here some of them have one dot. This one looks like it has two dots: these are called the nucleolus, which is an organelle found inside the nucleus that will produce ribosomes, and i said the other day that the cell is going to spend most of its time in interphase g1 is when it’s doing All of its jobs right producing proteins, so the most uh most of these cells here on our screen are also in interphase.

Two let’s just count them up real quick. I see this one one, two, three, four, five, six, seven, eight nine ten, 12, 13. 14. 15. 16 17. see where i’m going 18, 19, 20, 21. 22. I’M i’m staying away from the ones that look like they have the chromatids and the chromosomes that are starting to appear right. So all of the ones that have that ghosted kind of dense dna or genetic material that’s contained within the nucleus that’s going to be the dead giveaway that you’re looking at interphase let’s contrast interphase with a look of what prophase looks like notice that the prophase the Dna is starting that chromatin is starting to form chromosomes, but you’re still contained within what looks like, maybe the shape of a nucleus as that nucleus begins to break down. So this is prophase there’s, only a few that are actually in prophase. When you look at it. One two see this one, this one’s, probably prophase or it could be metaphase i’m, not sure, but go one. Two uh i’ll look over here. Three four five that’s i’ll go with five. Five yeah looks good good. So after interphase after prophase, we meet in the metaphase – and this is maybe the easiest one to identify uh it looks like the chromosomes are lined up along that metaphase plate in the center of the cell. So this is one two three four five. Six of them. You heard me say: maybe this one is metaphase, i can’t really tell some of them are kind of subjective.

So when you guys do this, for your lab it’s, okay, if you’re, not a hundred percent exact right on the money, uh yeah i’d say this is either prophase or metaphase i’m, not sure, because it’s hard to tell if that’s still a nucleus or if it’s lined Up along the middle, but after prophase metaphase you move into anaphase this that’s. What this looks like notice, the chromatids are moving to opposite sides of the cell. I see one here’s another one, two that’s really the only one i see and then take a look, telophase and cytokinesis so what’s the difference between anaphase and telophase. Remember that dna is now starting to uncoil. That chromatin is a little bit denser, so it doesn’t really necessarily look like they’re chromatids anymore, but the dead giveaway here is that that formation of that cell wall, if you look here, it looks like that kind of ghosted image between the two dense uh. What will become nuclei here looks like a cell wall and that’s what’s happening that cytokinesis process is going to cleave those cells into two let’s count up the number that are in telophase. This is one take a look this one down here. Two see that the dna looks like it’s starting to unravel it looks like it’s starting to be contained within a nucleus and, most importantly, it looks like that cell wall is starting to form so that’s, two ah here’s another one. Look at this three.

All right. I see i don’t see any others, oh right here, maybe kind of use. Your imagination see that that kind of an indication that there is a uh cell wall that is forming between this uh massive genetic material, all right. So what we’re going to do now is a lab that answers the question at the bottom of the screen. It says: assuming onion root cells, take 24 hours to complete the stages of interphase, prophase, metaphase, anaphase, telophase and cytokinesis. How long does each of those stages last and so there’s about 70 to 77 or so cells here in this image? And the number depends on if whether or not you include some of the cells that have been cut off like this one looks like prophase notice. The indication of the nucleus uh, but it’s been cut off, so if you want to include the cut off cells or not that’s up to you uh, these are probably an interphase over here, although it’s, you know we’re, not 100 sure since we can’t see it. Of course, there is a some instructions here for us, along with a lab handout. So let me pull that up. All of the instructions here are found on our day. 15 formative points cell cycle investigation, including this image here. So if you needed some more help with trying to identify the different phases, this is here for you and of course, i’ve got some instructions. Let’S let’s do that i’ll pull up that handout, as i show you the procedures, so you guys are going to use the image of the onion root on the handout also below to collect data on the number of cells in interphase, prophase, metaphase, anaphase, telophase and cytokinesis Record your data in the data table on the handout take a look we’re going to going to then determine the percentage of cells at each stage of the cell cycle by using the formula now i’ve.

Given you some examples here on how to do that, i’ll come back and actually show you what that might look like on the paper. So after we determine the percentage of cells at each stage of the cell cycle, we’ll determine the time spent in each phase and i’ll show you how to do that in a moment. I’D. Also, like you guys to describe your data, write a claim and reasoning statement and then turn in your work for some points. So let’s pull up this handout here all right, so that image is actually going to be found on the second page, but real, quick, just anywhere where there’s, yellow and those hashtags is where you’ll type you’ll write a claim. Of course, the claim answers the research question up here. Right i’ve got an evidence area and also some reasoning with some instructions on what to write exactly but let’s. Look at the second page and it’ll take a second to load. That image take a look at the data table on the bottom, so we’ve got the number of cells in interphase, prophase, metaphase, anaphase, telophase we’ll. Add all those numbers up to find the total now i’ll need these numbers here to determine the percentage of the cells in each one of those phases right here, right so that’s, where this equation is going to come into play the number of cells in any one Stage of the cell cycle, divided by the total number of cells in the photo we’ll multiply that by a hundred to move the decimal point over to to the right um, so count up right, uh, the vast majority look like they’re an interphase, so count them all Up imagine for a moment i’m making this number up let’s.

Imagine for a moment that there are 40. there’s, not there’s more than that but i’m, just making it up and imagine that uh there were a total of we’ll, say: 70 uh of those cells uh right their total number of cells right how again i’m making up This data, so how can i get that total you’ve got to find all of the numbers of all of these stages? First, but it’s, probably around 70.. So how do you figure out the um? The percentage of the cells in interface then well 40. Out of the total 70 are in interphase and so it’s an equation. Let me pull up some paper 40. Over 70 times 100 we’ll need a calculator 40 divide sine 70 equals that multiply by 100 to move that decimal point over and we get 57.14 again. This is i’m making it up the data i’m making up the data, but this is how you could do it yourself, and so what i’d like you to do, then, is go ahead and type that in here Music and then take a look all the way on This first page is another data table, of course, so we can transfer in those percentages as we start to calculate them and then to determine this. The time spent in each of those stages we’re going to multiply this percentage times the total length of time the cell took in each for the entire cell cycle 57 times 24.

That sounds like i’ll need a calculator of course we’re going to have to convert this back to a decimal point so 0.571 times 24 total, and so our answer then, would be 13.7 hours again. I’Ve made up this data but that’s what my expectation is for you guys to go through and tell me the actual percentages for each of these from there you’ll be able to write a claim and i’d like you to flesh out a nice reasoning statement. I want you to make some connections with the lecture for chromosomes with what we talked about with each of those stages, maybe even discuss why interphase, you feel is the longest of this of the stages and why the other ones are shorter. All of that information could go right in here all right.