Cell Division: Stages of Meiosis | A-level Biology | OCR, AQA, Edexcel
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- Опубліковано 17 тра 2024
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The key points covered of this video include:
1. Meiosis Overview
2. Prophase 1
3. Metaphase 1
4. Anaphase 1
5. Telophase 1 and Cytokinesis
6. Prophase 2
7. Metaphase 2
8. Anaphase 2
9. Telophase 2
Meiosis Overview
Meiosis is the process of creating haploid cells - it does this through two divisions. The first division - meiosis 1 - comes just after chromosomes have duplicated in interphase. In meiosis 1, homologous chromosomes are separated from each other. A short time after the first division meiosis 2 happens - in meiosis 2 the sister chromatids from each chromosome are separated. At the end of meiosis 2 we end up with 4 sets of genetically different cells, each with a haploid number of chromatids in them.
Prophase 1
Prophase 1 is the first stage in meiosis. The chromosomes supercoil, the nuclear envelope breaks down, and the spindle fibres form from the centrioles. Then the chromosomes undergo a process called crossing over. Crossing over is the exchange of DNA between chromatids on homologous chromosomes in prophase 1 of meiosis. In crossing over, sections of DNA are exchanged between homologous chromosomes. The homologous chromosomes line up and twist around each other. The wrapping can cause sections of chromatid to break off, they can then be swapped over to the homologous chromosome. Because the chromosomes are homologous, crossed over chromosomes have the same genes as before. Genetic variation is introduced in crossing over since all of the alleles are shuffled around on different chromosomes.
Metaphase 1
The next stage of meiosis 1 - metaphase 1 - involves chromosomes lining up at the equator. The first step involves the attachment of the chromosomes to spindle fibres by the centromeres. Each chromosome lies next to its homologous partner at the equator. Within the homologous pair, the chromosomes are randomly organised on either side of the equator - this is independent assortment.
Anaphase 1
The next stage of meiosis 1 - anaphase 1 - involves the separation of homologous chromosomes to opposite poles. In anaphase 1 each chromosome from the homologous pair is pulled apart to opposite ends of the cell. One out of the pair of homologous chromosomes will end up on each side - which of them it is, is random.
Telophase 1 and Cytokinesis
The next stage of meiosis 1 - telophase 1 - involves the separation of homologous chromosomes to opposite poles. Animal cells reform a nucleus for a short period after anaphase 1 in telophase 1. Animal cells also undergo cytoplasm splitting in cytokinesis. Plant cells on the other hand go directly into the next stage of meiosis without splitting.
Prophase 2
After meiosis 1 we are left with two sets of segregated chromosomes. In prophase 2 the DNA supercoils, the nucleus disintegrates and a new spindle fibres form. This is the same as mitosis - except that the chromatids on each chromosome are no longer identical due to crossing over.
Metaphase 2
In metaphase 2 the chromosomes line up at the centre through the attachment of spindle fibres to their centromeres. Chromatids are randomly assorted onto either side of the equator - they will be pulled to the poles in anaphase 2.
Anaphase 2
In anaphase 2 the genetically different chromatids are randomly segregated to opposite poles.
Telophase 2
After anaphase 2 the nuclei start to reform in telophase 2 and the cell splits in cytokinesis. In animals the two cells split in two - making four cells. In plant cells the nuclei aren't separated by plasma membrane yet, so the cell splits four ways to make four cells.
Summary
Meiosis involves the splitting of a diploid cell into four haploid cells in two phases
In prophase 1 homologous chromosomes cross over - shuffling the alleles
In the rest of meiosis 1 the chromosomes are independently assorted to opposite poles
In meiosis 2 the chromatids are separated to form four genetically different haploid cells
This is a confusing topic
LMAO IKR
Yeah it is
Fact, fr
FANTASTIC! THANKS THIS HELPLED SO SO SO MUCH, YOU MADE IT MUCH MORE CLEARER THAN MY BIO TEACHER COULD IN 3 LESSONS. PLEASE CONTINUE TO MAKE THESE FANTASTIC VIDEOS
That's great to hear! Will do! 😊
You c the part u explained about crossing over
I understood it but it appeared 2x which kinda confused me but then realized u were repeating the same thing.
Since chromosomes replicate i think u replicated a section of this video
thx anyway
LOLLLLLLL i was also thinking the same,i got confused too, anyway thanks now ik it was the same thing :)
He gave the example of replication by replicating the parts lmao
Yeh ahhaha I thought I’d accidentally rewound the video or something
This video helped me understand this so much better! Great for last minute cramming for my a level paper today... Thank you so much!
This is so helpful before having end of year exams!! Thank you so much
You're so welcome! Glad it was helpful!
I still find this topic confusing, but thank you as it I understand it much more now. :)
1:10 you said 26 instead of 46 by accident g
fr0g 23 pairs
This was really helpful. Thanks
Though meiosis a bit confusing, Thank you its so helpful 🙏
Great explanation
hi, the description of independent segregation completely contradicts a comment made earlier on-when talking about meiosis 1- in the video: at timestamp 3:18, you state " as we said, the copies from dad go in to one cell, and the copies from mum go in to the other cell". However when explaining independent segregation at timestamp 11:40 you explain how when lining up in metaphase 1, the line up is random, resulting in blue and purple chromosomes to be together....
yeh i noticed this, the statement at 3:18 is just straight up wrong
you SAVED ME thank you!! I didn’t understand at all when just looking at the book
Glad it helped! 🦸♂️
Thank you as always
That was really helpful for revision!! thank you :)
You're so welcome! Glad it was helpful!
So what’s he trying to Homologous pairs is 1 copy from dad and 1 copy from Mum joined together.After replication there is 2 copy’s of dad and 2 copy’s of Mum joined together right?
Amazing video, Thank you!!
You're welcome! Glad you liked it! 👍
Is this enough detail for a level?
Its great to be taught by you
Glad you liked it! 😊
Nuclear membrane disintegrates in prophase 1or in metaphase 1? I watched another video. I watched it disappeares in metaphase but u said it disappeares in prophase
prophase
After meiosis 2 when you say they “split” into 4 cells is it because of cytokinesis? Would you call that cytokinesis 2? Or do they just “split”
He says cytokinesis :)
yeah its because of cytokinesis there is no such thing as cytokinesis 2 :)
this video wasn't as clear as other videos u make can't lie
trust
This is super helpful but you missed stages like leptotene, zygotene, pachytene, and diplotene… anyway the video was awesome! 👏👍
don't think you need this for a level!
super sir...your videos are just awesome.....
Thank you so much! 😀
Mate I love you
💖
What does maternal and paternal mean ?
is this AS level?
Nope A2
Bob Jeff in IAL it’s AS level unit 2 so yes
Its AS level unit 2
AS AQA Topic 4
Yes
I think there are some mistakes early on in this video...Around Homologous Chromosomes early on. Easily done as it is complex.
Dear sir as i have studied from my teacher's, meiosis take place in gametic cell formation. Its separately take place in male and female to form sperm and ovam. How come in this video at meiosis during interphase you are explaining about dad and mom together?
females have DNA from their fathers AND mothers in their cells which is why he refers to it as the male DNA
Because human cells have chromosomes from the mother and the father. So when the cell divides, both mom's and dad's chromosomes will be present.
did this guy just repeat crossing over about 826 times
😅😅
Mum and dad? I thought meiosis is making more sex cells, so for a female it would be making more egg cells? Why are there mum and dad genes here?
Because your sex cells contain DNA
Because you have dna from mum and dad and it's your dna that splits into multiple sex cells
when you were born you got DNA from your mum and dad. so each homologous pair of chromosomes actually include one from your mum (maternal) and one from your dad (paternal). then when you make gametes, these chromosomes (with different genetic material) are put into different cells by meiosis in many different ways to create genetic variation. (okay sorry if i actually suck at explaining but hope you don't get even more confused by my explanation)
Ohhhhh thanks guys, that cleared it up :D
@@evie9748 this helped me so much thankyou !
You said we have 26 pairs???!
Audio is really quiet. Excellent otherwise
From my phone and laptop the audio is fine maybe it is your gadget?
@@rehnumachowdhury3629 Maybe. Works fine with other videos though.
yeah i agree the audio is relay low. the video was very useful.
Increase your volume
@@ashishzachariah1373 i cant believe i didn't think of that! genius.
why do you always say youll finish with a summary and never do a summary lmao
The videos with the summaries at the end can be found on our website snaprevise.co.uk. I suggest that you go and check it out! You can also find there some free resources like revision guides, quizzes, cheatsheets, and a lot more! 😊
46 pairs , not 26