Meiosis | Genetics | Biology | FuseSchool
Вставка
- Опубліковано 20 тра 2024
- Meiosis | Genetics | Biology | FuseSchool
There are two types cell division processes: Mitosis & Meiosis
The simpler one is Mitosis - which produces two identical cells with exactly the same genetic information. You can think of them as clones of each other.
The other process, Meiosis, is a much more complicated process creating not two but four cells, with only half the number of chromosomes and crucially all genetically different from each other.
Both mitosis and meiosis include the same phases - prophase, metaphase, anaphase, and telophase.
Except, in Meiosis, they happen twice, so they’re usually referred to as 1 and 2.
The easiest way to remember these phase names is to remember IPMAT: Interphase, Prophase, Metaphase, Anaphase, Telophase.
So let’s look at meiosis in more detail...
As always, cellular division starts with a process called DNA replication.
This involves making two identical copies of the original DNA molecule.
The cell ends up temporarily with double the normal number of chromosomes.
In prophase I, the duplicated chromosomes join up with the pair from the other parent - so the mother’s pair bind with the father’s pair, forming a group of two chromosomes called ‘homologous’ chromosomes.
As each chromosome is lined-up next to it’s partner pair, one chromatid from each side gets entangled with the corresponding chromatid from the other side. This is called ‘crossing-over’.
During this brief period, the two chromatids swap certain sections of DNA. This is called recombination. The sections that they trade correspond to the same location, so that each chromatid retains the correct number of genes.
Recombination is really important because it creates variety. The new cells aren’t identical to their parents, and they also are different to one another as well.
There are new genetic combinations.
In fact that’s the whole point of sexual reproduction!!! … to increase genetic variability.
Each chromatid is now different, and as each one will end up in a separate gamete, it means each sex cell is genetically different from all others! This explains why brothers and sisters are different despite having the same parents. Only identical twins have the same genetic make-up as they both originated from the exact same egg and sperm!
Now back to meiosis: next comes Metaphase I as the chromosomes align themselves up in the middle of the cell.
In Anaphase I, the spindle fibres pull the chromosomes apart, to opposite ends.
Then during telophase I and cytokinesis, the cell pinches apart in the middle and the nuclear membrane reforms around the two new daughter cells.
That’s the end of meiosis 1.
We start with our ‘recombined’ daughter cells, each still with 46 chromosomes.
But sperm and eggs cells only have 23 chromosomes, so we need to cut these cells in half...
The process is exactly the same as before, except that there is no DNA replication.
We start straight with Prophase II, with chromatin clumping again to form chromosomes. They align in the middle of the cell during Metaphase II, and chromatids are pulled apart during Anaphase II by the spindle fibres. Telophase and cytokinesis pinch the cells together, with four new granddaughter cells being formed.
The end of meiosis gives us 4 different sex cells, each with only 23 chromosomes. Ready for future fertilisation
CREDITS
Animation & Design: Bing Rijper
Narration: Bing Rijper
Script: Alex Reis
SUPPORT US ON PATREON
/ fuseschool
SUBSCRIBE to the FuseSchool UA-cam channel for many more educational videos. Our teachers and animators come together to make fun & easy-to-understand videos in Chemistry, Biology, Physics, Maths & ICT.
VISIT us at www.fuseschool.org, where all of our videos are carefully organised into topics and specific orders, and to see what else we have on offer. Comment, like and share with other learners. You can both ask and answer questions, and teachers will get back to you.
These videos can be used in a flipped classroom model or as a revision aid.
Find all of our Chemistry videos here: • CHEMISTRY
Find all of our Biology videos here: • BIOLOGY
Find all of our Physics videos here: • PHYSICS
Find all of our Maths videos here: • MATHS
Instagram: / fuseschool
Facebook: / fuseschool
Twitter: / fuseschool
Access a deeper Learning Experience in the FuseSchool platform and app: www.fuseschool.org
Follow us: / fuseschool
Befriend us: / fuseschool
This is an Open Educational Resource. If you would like to use the video, please contact us: info@fuseschool.org
You really just summarised what i failed to understand for weeks in 5 minutes. Saved me from failing my test. Thanks g.
No worries! Glad it helped! 👍
same
For those who wonder about "Father"/"Mother" pairs/chromosomes - Our chromosomes are built from a combination of F&M (Father & Mother) chromosomes (Literally, from our mum and dad), which means that in each pair we have 1F and 1M. When the pairs duplicate, we have 2F and 2M. Two pairs of our pair.
In other words -
Our pair = 1 F & 1 M
During duplication = 2 F & 2 M
Now, each time the cell going through meiosis is about to divide (not duplicate!), the DUPLICATED F&M chromosomes get entangled, or mixed if you will, thus creating something new, even if by tiny changes.
It took me a while to grasp as well until I realized what "Father" and "Mother" meant.
The biggest problem with these kind of videos is that when talking chromosomes, context is highly important when explaining meiosis and mitosis as chromosomes act slightly differently in each process. For some learners, this is a nightmare because teachers don't differentiate between chromatids and chromosomes when they speak (Knowing to speak correctly for a teacher is as important as knowing the subject itself).
At 1:35, the narator implies that there are now "The double number of chromosomes" after the DNA duplication and shows the number 46 (which is rather confusing). This is a linguo trap (or shortcut) that many, many teachers easily fall into because they already are very familiar with the whole process and don't think twice about it (as evidenced by the "46 chromosomes in total instead of 23" anwser that FuseSchool has given in some anwsers). For students this is problematic, because you just learned a week ago that there are already 46 chromosomes (23 pairs) in a somatic cell to begin with, so how does duplication (doubling) not make 92 chromosomes? Saying that we now have 46 pairs implies (that's the way our brains interpret sentences) that we only had 23 chromosomes (11.5 pairs?) before the duplication, which does not make any sense. When you're a teacher, this is critical because 1 minute in your explanation, you already have lost the students because you made a logical language mistake (as evidenced by many similar questions in this comment section).
Explanation: Chromosomes have duplicated and unduplicated states. During DNA duplication, chromosomes go from unduplicated to a duplicated state. As the name implies, it's the DNA material that is duplicated. The number of chromosomes stays the same. Every single of the 46 chromosomes we began with are still one chromosome each, but they now have double the DNA material or information (chromatids, the little "arms"). The process started with 46 unduplicated chromosomes and 46 chromatids to 46 duplicated chromosomes and 92 chromatids. If you draw this visually, there are now 46 pairs, but the number of chromosomes is unchanged. We do have 46 pairs, but these 46 pairs are not 46 pairs of 92 chromosomes, but 46 pairs of 92 chromatids. Saying that there are now 46 instead of 23 is misleading because it implies that what we started with (46 chromosomes in pairs of 2) is now 92 chromosomes in pairs of 2.
To make it easier, you can conceptualize with fruits.
You have 46 fruits (23 given by your mom and 23 given by your dad) of a single type each (1 apple, 1 orange, etc). You decide to classify them by color, size and shape. Because nature is incredible, you note that, of these 46 distincts and unique fruits, you can make 23 pairs of very very similar fruits (color, size, shape). Following this natural casslification, you don't have more or less fruits. You still have 46 single, unique fruits (with 22 pairs of them being very similar and the 23rd being a little weird). 46 fruits = 46 types of fruits.
For a weird experiment, you unclassify your neatly organized 23 pairs of fruits. You decide to perfectly clone each fruit you have on hand. You now have 92 fruits (2 apples, 2 oranges, etc) but still have 46 types of fruits. The only thing that has changed is that you have 2 perfectly identical copies of each type of fruit. So, while we still have pairs, they're not the same pairs we talked about in the begining. They're pairs of 100% identical, cloned fruits, not pairs of very similar but distinct fruits. Hence, saying we now have 46 of what we had 23 in the beginning is misleading because we're not pairing the same thing.
thank you so much for the explanation! i've been struggling with this one for a while
thank you :*
This saved me hours of research and now instead of Reding 3 chapters from my biology book, I'll just watch and enjoy this 5 minute video ! Thank You Fuse School, you rock !
bro you’re saving my a level one video at a time, bless u
Always happy to help 😉
Can't believe I learned it in just 5 minutes 👏👏👏
Wow man you made my concept clear! When I passed out of school, I wasnt habituated with youtube. thank you very much for these kind of pictorial explanations.
You're very welcome! Happy to help 🙂
Cheers, really appreciate the simplified explanation, textbooks can be very confusing
No worries! Hope it helped!
Now ready for this section in the exam
I think you’ve saved me from failing my test and homework… I could not comprehend what homologous chromosomes actually were until now. Thanks!!
Wonderful! Glad we could help 🤗
Helped me a lot. I am from India and I have taken up biology in class 11. Your videos always help me.
Life saver.
Thanks again
Subscribed too !
Thank you so much! Glad you find them helpful!
I DON'T Understand at 3:48 why the daughter cell has 46 chromosomes, shouldn't it be 23 chromosomes each?
Doesn't Meiosis II start with two haploid parent cells with 23 chromosomes each, not 46
Yup, you are right.
@@fuseschool you should clarify that in the description, I almost lost my mind
@@FBWUniverseMode SAME, just spend an hour trying to figure out how telophase 1 resulted in 2 cells each with 46 chromosomes 🥴
so basically meiosis goes through the same phases as mitosis. however happens twice but the second time it happens it doesn't go through interphase but before the changes, the chromosomes mix with each other changing the DNA then interphase starts by doubling then, prophase is when the spindle fibres appear, then metaphase is when the nucleus membrane disappears and the spindle fibres connect with the chromosomes and a line them on the equator of the cell then anaphase happens and the spindle fibres are shortened disconnecting the chromatids then telophase happens and the nuclei membrane surround the chromosomes and then finally cytokinesis is when both of the nuclei move at opposite direction splitting the cytoplasm and that happens again but without the interphase (which is to multiply) and you get gametes which are sex cells
BIG CHUNGUS POGGERS
dude idk what to say i watched many vids but to no help ur vid really made me understand like it was simple with no excessive animation and good explanation thank you
Thank you! Glad you found it useful!
Best video I've seen so far right up to the point where you have made a mistake During meiosis 1 the homologous pairs of chromosomes are separated so that at the end of meiosis 1 the two cells are haploid. They have 23 chromosomes each and not 46. During meiosis 2 the sister chromatids are separated so you don't half the number of chromosomes again, you simply separate the chromatids to produce 4 haploid daughter cells. Real shame ... lovely video up to the end of meiosis 1. You then give the impression that the reduction division is during meiosis 2 but it actually happens during meiosis 1.
You are right! Thanks for your comment!
So are you saying that the cells started with 23 pairs - when the DNA duplicated there are then 46 pairs - So each daughter cell at the end stage of meiosis 1 - after telophase and cytokinesis- have 23 pairs of chromosomes . Then in meiosis 2 the cells split again to end up with only 23 chromomes - all 4 haploid daughter cells.
Really helpful!! I like how everything was concisely and effectively explained.
Thank you! Glad you liked it!!
this is the first video, that helps me fully understand the process of meiosis. Thanks for creating it! ;)
Most welcome! Glad we could help!
Nice one
Thank you for this video...I really learned a lot...you simplify all of the terms without you getting my brain to explode....thank youu😌😌
Wonderful! Glad you found it helpful!
Thank you so much sir😊😊
bravo!!like only in 5 mins u covered what my teacher did 4 2 weeks
So I'm kind of confused. If There were 46 chromosomes and then the cell divided twice, shouldn't there be 11.5 chromosomes in each of the 4 cells? And if there are 23 chromosomes, then doesnt that meant there was actually 92 chromosomes to begin with? 92/4 = 23.
Thanks
Educational！
Thank you so much for your help 🙏🙏
You're so welcome!
Plz make more videos differentiating between mitosis and meiosis
Cool accent and content = )
Where do the 2 types of chromosomes come from in prophase 1, where you stated the mother chromosome line up with father chromosomes?
Same question here
I had the same doubt
But i concluded.........The 2 types of chromosomes in someone's sex cells would be from their parents which would undergo crossing over and form 4 types of cells
Thank you for clear my doubt
Happy to help
Thank you so much.
No worries!
Thank you very much, you people are great!
Thank you too! 🤗
So because of DNA REPLICATION changes are arrise and from mitosis form exact DNA copying and clones form.
THANK YOU OMG 👏🏽👏🏽
No problem!!
Love from India. Very nice presentation 💛
Thank you so much!
It was really helpful 👍🏻
Glad you think so!
Amazing video well explained!
Glad you liked it!
that was extremely useful I was to confused thank you
No worries! Happy to help!
Thanks 🙏🏻
No problem 👍
Good video thanks👍👍
No problem 👍
I thought that meiosis I is referred to as a reduction division for the simple fact that the number of chromosomes in the parent cell are reduced by half so in essence meiosis II should start with 23 chromosomes, and not 46?
Yes, that’s what I think too. At the end of Meiosis 1 there are two haploids, so each cell has 23 chromosomes. Then, in meiosis ll the chromatids are pulled to each opposite end making 4 haploid cells. This is confusion because to count the number of chromosomes, you count the amount of centromere’s present.
U guys are the best!!
Thank you so much 💜
Thank you sooo much. What I'd give for my bio teacher to be you
You are most welcome!
thank you!!
No worries!
Thanks a lot 😊
No problem 😊
@ FuseSchool
Keep posting 😊
Hay, you have not added End Screen....
May i ask is the chromosome number doubled at anaphase II when the sister chromatids are separated by the spindle fibre? Thanks!
As you said, at anaphase II sister chromatids separate. They are now called sister chromosomes and are pulled toward the centrioles. This division is known as an equational division, because each cell ends up with the same quantity of chromosomes as when the division started, but with no copies.
(ref: biologydictionary.net/meiosis/#)
@@fuseschool Thanks a lot for the video and especially for the reply!
Happy to help!
how do the 4 daughter cells have 23 chromosomes each when they are divided please explain.
well that was very helpfull thank you
You're most welcome!
does this include A level content
Did anyone realise that the sentence 'but that's a story for another video' (at 4:34 ), is from the chanel 'What if' ?!
I think im just really dumb by im trying to understand really badly, where does the father dna come from
penus
I had the same doubt......But i concluded.........The 2 types of chromosomes in someone's sex cells would be from their parents which would undergo crossing over and form 4 types of cells
leventhorpe?
I think it should be clarified that in this example model, the organism you're working with has 2 chromosomes. A big and a small chromosome, just so it's unambiguously clear. A lot of bio texts gloss over this in their examples.
wow awesome
Thanks 🤗
This helped
Great!
After meiosis I, are there not 23 chromosomes in each daughter cell?
Yes, you are correct.
@@fuseschool yessss. It was wrong...i was looking for this comment
during interphase, the number of chromosomes is 46 pairs or just 46?
This might help: www2.le.ac.uk/projects/vgec/highereducation/topics/cellcycle-mitosis-meiosis
@@fuseschool thank you for ur response :))
Perhaps, I'm the first commenter
lol these videos r why im not gonna fail ig bio
Always happy to help!
Still don’t get it
same
in Iraq we study the cell even
Wait so when the dna duplicates in the first stage is there 92 chromosomes in the cell/46 pairs. I’m so confused
there’s 46 chromosomes and 23 pairs
46 chromosomes in total, instead of 23 🙂
The biggest problem with these kind of videos is that when talking chromosomes, context is highly important when explaining meiosis and mitosis as chromosomes act slightly differently in each process. For some learners, this is a nightmare because teachers don't differentiate between chromatids and chromosomes when they speak.
At 1:35, the narator implies that there are now "The double number of chromosomes" after the DNA duplication and shows the number 46 (which is rather confusing). This is a linguo trap (or shortcut) that many, many teachers easily fall into because they already are very familiar with the whole process and don't think twice about it (as evidenced by the "46 chromosomes in total instead of 23" anwser that FuseSchool has given to your question). For students this is problematic, because you just learned a week ago that there are already 46 chromosomes (23 pairs) in a somatic cell to begin with, so how does duplication (doubling) not make 92 chromosomes? Saying that we now have 46 pairs implies (in the minds of students) that we only had 23 chromosomes before the duplication, which does not make any sense. When you're a teacher, this is critical because 1 minute in your explanation, you already have lost the students because you made a logical language mistake (as evidenced by many similar questions in this comment section).
Explanation: Chromosomes have duplicated and unduplicated states. During DNA duplication, chromosomes go from unduplicated to a duplicated state. As the name implies, it's the DNA material that is duplicated. The number of chromosomes stays the same. Every single of the 46 chromosomes we began with are still one chromosome each, but they now have double the DNA material or information (chromatids, the little "arms"). The process started with 46 unduplicated chromosomes and 46 chromatids to 46 duplicated chromosomes and 92 chromatids. If you draw this visually, there are now 46 pairs, but the number of chromosomes is unchanged. We do have 46 pairs, but these 46 pairs are not 46 pairs of 92 chromosomes, but 46 pairs of 92 chromatid. Saying that there are now 46 instead of 23 is misleading because it implies that what we started with (46 chromosomes in pairs of 2) is now 92 chromosomes in pairs of 2.
To make it easier, you can conceptualize with fruits.
You have 46 fruits (23 given by your mom and 23 given by your dad) of a single type each (1 apple, 1 orange, etc). You decide to classify them by color, size and shape. Because nature is incredible, you note that, of these 46 distincts and unique fruits, you can make 23 pairs of very very similar fruits (color, size, shape). Following this natural casslification, you don't have more or less fruits. You still have 46 single, unique fruits (with 22 pairs of them being very similar and the 23rd being a little weird). 46 fruits = 46 types of fruits.
For a weird experiment, you unclassify your neatly organized 23 pairs of fruits. You decide to perfectly clone each fruit you have on hand. You now have 92 fruits (2 apples, 2 oranges, etc) but still have 46 types of fruits. The only thing that has changed is that you have 2 perfectly identical copies of each type of fruit. So, while we still have pairs, they're not the same pairs we talked about in the begining. They're pairs of 100% identical, cloned fruits, not pairs of very similar but distinct fruits. Hence, saying we now have 46 of what we had 23 in the beginning is misleading.
Kian
this vid was sik
epic poggers moment
not a big fan sorry