Homologous Chromosomes vs Sister Chromatids Explained!

[Music] everyone dr. D here in this video I'm going to show you the difference between homologous chromosomes and sister chromatids so this is very important to understand especially for chapters 10 and 11 we're going to be covering mitosis and meiosis and the better you understand the difference between homologous chromosomes and sister chromatids the better you're going to do with your understanding and the easier it is going to be to understand those concepts so what is a Hamal what are homologous chromosomes as you know humans have 46 total chromosomes right humans have 46 chromosomes total but you inherited 23 of those from your dad and you inherited 23 from your mom all right I'm gonna use blue for dad red for Mom okay the egg from your mom's egg the egg housed 23 chromosomes one chromosome one one chromosome two one chromosome three one chromosome four you get the idea 23 different chromosomes the sperm from the dad housed 23 chromosomes as well this included a chromosome one a chromosome two a chromosome three so every person then has 46 total chromosomes but they actually have two sets of chromosomes so what's a set a set means 1 through 23 having chromosomes one chromosome two chromosome three comes on for a set of chromosomes 1 through 23 that's a set so you inherited a set from your dad and you inherited a set from your mom and so you have two sets of chromosomes you know what that means that means let me draw chromosome one for example let's say this is chromosome 1 from your dad you also have a chromosome 1 from your mom now both of these are called chromosome 1 okay both are chromosome 1 but are they identical if you were to sequence the DNA would it have the exact same sequence no that one's from your dad and that one's from your mom that your mom and dad are not related so they are not going to have a similar DNA they're not it's not gonna be the exact same so these are not the exact same chromosome they're they don't have the exact same sequence but they're both called chromosome 1 ok why are they called chromosome 1 they're both chromosome 1 and you have two chromosome twos and you have two chromosome threes and you have two chromosome force so what constitutes the chromosome number well here's the thing these two do have something in common but it's not the exact same sequence what they have in common is that the same types of genes that are on this chromosome are found on that chromosome does that make sense you remember what chromosomes are chromosomes are one continuous piece of chromatin or DNA one continuous piece and remember the chromosomes house the genes right there are genes along the chromosomes each chromosome contains thousands or at least hundreds I should say hundreds of genes on each chromosome all right so whatever genes appear on this chromosome 1 also appear on that chromosome 1 for example if I color the gene for eye color was on this chromosome it would also be on the other chromis one okay if there's if haircolor was on this chromosome one from mom it would also be on that chromosome one from your dad so so what we could say is the same types of genes appear on these chromosomes but not the exact same sequence okay so again you have two chromosome ones two chromosome two is two chromosome threes but they're not identical ones ones from your mom wants from your dad but what they do share in common is that they share the same types of information the same types of genes okay and and there's a term for this you see how there's the paternally inherited from your dad and the maternally inherited chromosome one they are called homologous chromosomes okay homologous chromosomes homologous chromosomes are not identical homologous chromosomes share the same chromosome number but remember one was inherited from your dad one from your mom so they are they should they have the same types of genes on there but I citing types of information but they're not identical okay now again you've inherited 23 chromosomes from your dad 23 chromosomes from your mom you have two chromosome ones two chromosome two is two chromosome threes okay now what happens if the cell wanted to divide right a normal cell has 46 chromosomes right well what if that cell wants to divide into two cells well it can't just go ahead and divide because if if a cell went ahead and two just went ahead and divided each new daughter cell would have 23 chromosomes does that make sense that's not good you don't want your you don't want your daughter cells to have 23 chromosomes each if if one cell divides into two you want it to divide so that it's it retains its 46 chromosomes so in that case you know what you need to do before the cell divides before the cell divides you need to copy all the DNA don't you need to copy all the chromosomes so for example if this is dad's chromosome one you need to make a copy of it you need to have two dads chromosome ones right see you make a copy of dads come someone so these are now identical copies of dad's chromosome one and then you also need to copy mom's chromosome one you see that you need to make a copy of that as well so this is an exact carbon copy of mom's chromosome one now you have two of moms come as on one two of dads chromosome one and you're gonna have a copy of all your 46 different chromosomes so how many total chromosomes do you have at this point you have 92 total chromosomes right 92 that way that way if you were to divide at this point you would have 46 46 you'd be back where you started which is what you want okay there's a term for this you need to understand this you see how now you have a copy of every chromosome those copies have a very specific name those copies are called sister chromatids okay sister chromatids are identical in every way sister chromatids are identical in every way sister chromatids and here's the thing a normal skin cell doesn't have sister chromatids right it just has 46 chromosomes one set from mom one set from dad okay the only time a cell has sister chromatids is when the cell is about to divide the cell has considered it is about time to divide the cell into two at that point it makes a copy of all the 46 chromosomes and all at that point do you have sister chromatids okay so hopefully this was helpful you should definitely definitely understand the difference between homologous chromosomes which are not identical one was inherited from mom one was inherited from dad they shared the same chromosome number because they have the same types of genes and then the difference between that and sister chromatids which only exist after the DNA has been replicated by the way foreshadowing this is going to happen during S phase of interphase okay only at that point do you have a sister chromatids okay so I hope this helped let me know if you have any questions below and thank you for watching [Music]

Channel: Dr. D. Explains Stuff

Views: 57,401

Keywords: Homologous Chromosomes, Sister chromatids, Homologues, Difference between, Dr. D., Dr. D. Explains Stuff, Explained!, Explained, Biology, Mitosis, Meiosis

Id: wbqbNpthLeg

Length: 9min 46sec (586 seconds)

Published: Wed Nov 14 2018