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A2 Biology OCR June 2015 Revision Thread

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Original post by frozo123
are chromosomes made up of DNA then?
so the 46 chromosomes, one chromosome from the father, one from the mother? 23 pairs?

but in haploid cells, the number of chromosomes have been halved so there's 23 chromosomes in each cell? how do they pair up?
and then how do they half again? ( not the process) but the concept of n
lol so confused


Yes, they are.
That's correct, you have 23 chromosomes from your mum and 23 from your dad.

Yes that's true, in haploid human cells there's 23 chromosomes in each cell. Okay I'll be honest you're even starting to confuse me a bit now :tongue:are you asking about meiosis? If you are then I'd recommend going over meiosis I and II as I think that's what you're asking about.
Original post by smozsolution
Yes, they are.
That's correct, you have 23 chromosomes from your mum and 23 from your dad.

Yes that's true, in haploid human cells there's 23 chromosomes in each cell. Okay I'll be honest you're even starting to confuse me a bit now :tongue:are you asking about meiosis? If you are then I'd recommend going over meiosis I and II as I think that's what you're asking about.


okay cool rings a bell, well I understand all of prophase,anaphase etc
but gametes undergo meiosis twice don't they? they start off with 46 chromosomes, so the 2 haploid cells produced will have 23 chromosomes each? then apparently they divide again by meiosis? so does that mean each cell has11.5 chromosomes each?
EDIT: Nevermind sorted it out haha
(edited 9 years ago)
Original post by frozo123
okay cool rings a bell, well I understand all of prophase,anaphase etc
but gametes undergo meiosis twice don't they? they start off with 46 chromosomes, so the 2 haploid cells produced will have 23 chromosomes each? then apparently they divide again by meiosis? so does that mean each cell has11.5 chromosomes each?
EDIT: Nevermind sorted it out haha


They undergo mitosis twice, of which chiasmata and independent assortment give variation.

The double stranded chromosome you so commonly see are chromosomes after interphase, which means at that point (prophase 1), you have 86 sister chromatids. The double stranded chromosome is one chromosome from either parent that's been replicated, which is why during normal anaphase, when the spindal fibres contract and separate the double stranded chromosome both cells are identically the same
Original post by tewas
do we need to know sickle cell anaemia in detail? and what do we need to know about homeobox genes? so much to learn so little time


No I don't think we do need to know sickle cell anaemia in detail because its not actually on the specification. I've only ever see it come up in context of the gene tables e.g. all the estates stuff but you don't really need to understand sickle cell anaemia for that all you need to understand is how to do the gene tables
Original post by miyah24
Hi guys I want to know some ways to remember all the biology content, because I keep forgetting it.


i first make good detailed notes and then from that I go over and over and over them and summarise or re-write some stuff out or draw diagrams and annotate and then I test myself and do some exam questions on that specific topic so I can see if I have really understood

I also make flash cards as they are good way to practice summarising and getting the key points down plus you can carry them everywhere so can look at them always
Original post by tewas
do we need to know sickle cell anaemia in detail? and what do we need to know about homeobox genes? so much to learn so little time


I think we need to know and recognise that sickle cell anaemia occurs in the b polypeptide chain of haemoglobin. It is due to a substitution mutation- changes one amino acid which alters the 3d structure of the protein- therefore can no longer carry O2

For homeobox genes we need to know that they are homologous within kingdoms and not between kingdoms (e.g animal homeobox sequences not the same as fungi or plants)

I also learnt how homeobox genes control development (i.e code for homeodomains which specifically bind to DNA- producing transcription factors) but i dont know if this is required- understanding concepts helps me to remember things!
Original post by kwaddell16
I think we need to know and recognise that sickle cell anaemia occurs in the b polypeptide chain of haemoglobin. It is due to a substitution mutation- changes one amino acid which alters the 3d structure of the protein- therefore can no longer carry O2

For homeobox genes we need to know that they are homologous within kingdoms and not between kingdoms (e.g animal homeobox sequences not the same as fungi or plants)

I also learnt how homeobox genes control development (i.e code for homeodomains which specifically bind to DNA- producing transcription factors) but i dont know if this is required- understanding concepts helps me to remember things!


do you really think we need to know that for sickle cell anaemia? I thought if they would ask a question on they would give you all the info you need and then ask you to pick out stuff you do know e.g. what you just said about mutations or what i previously said about gene tables
Anyone else been focused on f214 revision up until now? Planned to start on f215 after the Easter break, but it seems like everyone on this thread is already well into f215 revision :s-smilie: Stress!
Why OCR made Biotechnology so long only God knows. I hate it so much.
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Original post by sarahelizabeth18
Anyone else been focused on f214 revision up until now? Planned to start on f215 after the Easter break, but it seems like everyone on this thread is already well into f215 revision :s-smilie: Stress!


Mainly did revision for the first exam ready for mocks last January and a lot has stuck in my mind :smile:

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Original post by spookz
Why OCR made Biotechnology so long only God knows. I hate it so much.


GOSH! SAME! i even slightly prefer the Plant bits! but biotechnolgy F*** it goes on forever!
Original post by phoebc
do you really think we need to know that for sickle cell anaemia? I thought if they would ask a question on they would give you all the info you need and then ask you to pick out stuff you do know e.g. what you just said about mutations or what i previously said about gene tables


i dont think we have to learn it all- you just have to know it is an example of a type of gene mutation (e.g substitution) and then apply biological knowledge

e.g- change in amino acid= alter in 3d structure

:smile:
Original post by ChoccyPhilly
They undergo mitosis twice, of which chiasmata and independent assortment give variation.

The double stranded chromosome you so commonly see are chromosomes after interphase, which means at that point (prophase 1), you have 86 sister chromatids. The double stranded chromosome is one chromosome from either parent that's been replicated, which is why during normal anaphase, when the spindal fibres contract and separate the double stranded chromosome both cells are identically the same


does chiasmata mean the crossing over and twisting of chromatids?
don't you mean 92?
yeah I understand now thankyou so much! I was just half asleep and missed the sentence of replicating then I got so confused haha
Does anyone else feel like unit 5 goes on forever?
Original post by frozo123
does chiasmata mean the crossing over and twisting of chromatids?
don't you mean 92?
yeah I understand now thankyou so much! I was just half asleep and missed the sentence of replicating then I got so confused haha


Haha yes, I meant 92 :smile: and yes, chiasmata is when homologous chromosomes line up with one another and there are some cross overs between the two chromosomes at this point
Original post by smozsolution
Does anyone else feel like unit 5 goes on forever?

Yeeeep. It's horrible how long it is :/
Original post by AnnekaChan173
Yeeeep. It's horrible how long it is :/

At least the ecology chapter is small!
Original post by AnnekaChan173
Yeeeep. It's horrible how long it is :/


You get to the end of one long module and realise there's still loads to come :eek:
Original post by ChoccyPhilly
Haha yes, I meant 92 :smile: and yes, chiasmata is when homologous chromosomes line up with one another and there are some cross overs between the two chromosomes at this point


cool, thanks bro
Original post by ChoccyPhilly
At least the ecology chapter is small!


Ikr, thank god for that


Original post by smozsolution
You get to the end of one long module and realise there's still loads to come :eek:


Right!? I thought "You know it's okay, I just have one chapter to go (purple book) And I saw the size of 2.4 and wanted to shut the book
So you need an A* for your offer?

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