F215 - Revision thread 13th June 2011

lol my teacher too, and everyone on the thread do you think it's worth looking over last year's biology's Conservation module, theres so much to revise in this module anyway

Okay, in a cell, you're right - you have a paternal chromosome and a maternal chromosome. In interphase, they look like this:
| |

Then, in interphase, they replicate so that they look like this:
X X

In prophase, those two homologous chromosomes line up and form the bivalent like you said. They'll cross over, and the genes will get all mixed up ready for the divisions.




For the haploid/diploid thing, I think about it as a cycle:

Adult human - 2n ||
a chromosome from the mother, and one from the father
|
|
v
Gametes - n |
meiosis occurs, so that there is only half the genetic material - this will be a mixture of genes from the individuals parents
|
|
V
Zygote - 2n | |
gametes from the two parents join together, and then it starts again.

The ones endorsed by OCR. Surely if they are endorsed by OCR, then they are the correct ones (or so my teacher likes to bang on about)

Do the exam board print their own definitions?

I think I'm in love. Thank you!

So when you have:

X X, and then they line up, so when they get pulled away it have either the replicated pair from the mother, or from the father? With the chiasma, if any have crossed.

I then don't quite understand how independent assortment comes into play, well, ish. So if there were say, 5 pairs of chromosomes, so you'd have 5 bivalents? then in the first division you could get any combination of maternal/paternal chromosomes in each?

And finally, I promise it's becoming clearer, the difference between the chromosome/chromatid? Is the chromosome the X, and the chromatid is one half of the X? Then in the second division it's just the chromatids being pulled to each pole, as opposed to an X?

Thanks

Hey all,

I know the function of restriction endonuclease and what it does etc and I know it targets the restriction site on an DNA section, BUT does the enzyme have a complementary base sequence to the restriction site which has a specific base sequence (like DNA probe), or is it like all enzymes and has a particular active site and nothing to do with bases?

Can someone tell me why on modernisation online it seems to have written CHANGED under F214 and F215 and they no longer come up under the normal search only when specified by their keys??? I'm pretty sure this was done recently and I'm worried they might have done something to the exams we're going to be sitting in a couple of days.

I know its extremely hard to tell/predict, but does anyone have any ideas on what they think might come up on monday?

Yep - when they get pulled away, one chromosome from ecah homologous pair goes to each pole. With the crossed over parts etc. BUT, its one chromosome pulled to each end, not pair. They are a pair of chromosomes when they are lined up next to eachother, but only one is pulled to each end.




We'll use the crosses again:
X X
X X
X X
X X

If you have four chromosomes, they could arrange themselves like that ^ or they could arrange themselves as below. So once they are pulled apart, there will be different chromosomes in each of the new cells.


X X
X X
X X
X X

Independant/random assortment is the way of saying they go into the middle, but it doesn't matter what order, or what side the maternal/paternal chromosomes are on.




Yep, chromosome is X OR | before it has replicated.

And the chromatid is just one half of the X, so each chromosome (when replicated) has two chromatids.

In the second division, one chromatid is pulled to each pole, BUT when its separated, its called a chromosome again. So when its part of an X, the > is called a chromatid, but once its separate, its called a chromosome.

no no no, restricion enzymes are just like any other enzyme, they don't have bases.
And it wouldn't make sense them having coplementary bases as DNA is double stranded so it wouldn't have any un-bonded bases to bind to.

Someone please please please explain LINKED GENES!!! and how they work in a cross?