F215 - Revision thread 13th June 2011

Well my offer's ABB , noo failing we're going to Manchester! Good luck!

Haha ahright ok thank you x

No probs x

Hows revision getting along?

Im sat on the computer, going through random bits from the book, reading computer notes and god knows what else. All over the place

This is really badly stressful. Not healthy at all!

Not too good
I've made my own notes, basically filled an a4 notebook and now I'm typing them up, I've done a past paper and been reading over bits aswell, but none of it's really going in And I'm scared that even if I know the module inside out, all the application and synoptic questions will throw me off

Ahh I know I'm so stressed! Not long and it'll be over though
What grade are you aiming for?

Epistasis is really simple, you have two separate genes at two different loci (different parts on the chromosome) and the presence of a certain allele of one gene stops the expression of the second gene.

It'll be easier to understand with an example; so if it was fur colour in mice and you have an allele for Brown (B) and white (b). So the presence of the B allele will give a brown coat as it is dominant.
Now a completely different gene has two alleles A & a. Now for the Brown fur colour you need to also have the dominant A allele present so;
BBAA = brown
BbAA = brown
BBAa = brown
BbAa = brown

BBaa = white
Bbaa = white
bbaa = white
bbAa = white
bbAA = white

if the dominant A is not present the coat colour is white. This is recessive epistasis because if there are only the reccessive alleles it supresses the epression of the other gene. So, regardless of whether or not there is the dominant B for brown fur, if there is no dominant A the brown will not be expressed and the fur will be white.

A way to remember it so it makes sense is that the dominant A gene codes for an intermediate compound e.g a colourless pigment, and the B allele changes this intermediate into the final brown colour. If the intermediate is not present the B allele cannot have its effect.

Then dominant epistasis is just the reverse, so If here is the presence of a dominant allele at one loci, the second gene wont be expressed, so you need to have BOTH the recessive alleles for it to be expressed.

Im going to go crazy with past papers from today afternoon onwards. Then whatever i dont know which reflects through my answers, i'll just learn from mark schemes. Heads absolutely killing. Does yours hurt?!

Yep, i think eco system questions will trip me up. The topic is easy to learn but questions i find a little So stressed. I keep thinking of monday at half 1 sitting with the paper staring in my face aaaaaahhh

Im aiming for an A hopefully. You?

Yeah it does! I keep taking pro plus in the nights aswell, which probably doesn't help
I'm okay on ecosystems I think, it's just the long questions like meiosis/PCR/pretty much all of biotechnology and gene technologies, I always get them mixed up
Arghhh I know, I'm never usually this nervous for exams

Aw good luck, I'm sure you'll get it I'd like an A but I don't think it's going to happen, so I'm aiming for a B/high B I think. Although I worked out I only need 70 UMS in this exam to get into uni, which takes the pressure off a bit

what does 5' (prime) end and 3' (prime) end mean in PCR? (page 170)

Haha i manage to stay awake without proplus so i dont take it. Then i die in the morning 'cos ive stayed up half the night

Even though biotechnology was the hardest (IMO) to revise for 'cos its content heavy, i prefer questions on that. Specific. I cant even think in eco systems. Dont know what to write!

Thanks & im sure you'll get your B too How did you do in Jan if you dont mind me asking?

Im meant to be doing some bits of chemistry, but too traumatized about this!

Really well explained

Just a little confused with your example above. Do you need A and B together (both dominant) for brown fur?

What is a tropism? Proper definition?

Tropism is a directional growth response which is determined by the direction of the external stimulus

Haha, yeah i wish i didn't need sleep

Yeah i get what you mean, the ecosystems stuff is hard because you can go on about predation and competition and pretty much anything but the mark schemes are so specific if you don't say a certain word you don't get the mark :/

Thanks! I did so so badly in january, got a U I thought the paper was horrible, but tbh it was probably down to me revising loads for my other exams and not bothering with biology at all I'm resitting it though, and after doing this module it seems so much easier and i understand it all How about you?

Aw I'm so glad i don't do chemistry! I've heard it's so hard
What are you doing in uni next year, if you're going?

Yeah. You need to have dominant B for brown fur because that is the gene that codes for the brown. The other dominant gene A lets the second gene be expressed, so regardless if you have B or b if you don't have dominant A you will not get brown fur.