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Bio A2 Edexcel, natural selection

Ok, i've just about had enough of biology, but who can attempt to explain to me:
Stabilising selection, disruptive selection, directional selection.
and the stupid graphs they use
Please help before i rip up my notes in stress!
Reply 1
Avatar for ossoss87
ossoss87
3
lol... i hate A2 BIO!!!!!!!! bio is a bitch....
i dont have any notes... and i didnt even read it!! *am soo gonna fail!*
do u have any notes for unit 5?!?
Reply 2
Avatar for sahsum
sahsum
OP
13
yeh my teacher gives us o many notes that why there all so hard to learn!!!if u dnt have any have a look on www.s-cool.co.uk its quite good for biology!!what did u get at AS?
Reply 3
Avatar for dinesh
dinesh
I am sure you probably know what a Normal distribution is.
So the curve is symmetrical, with the mean being the mode.
That is stabalizing selection.
WHen the curve is skewed to one side, like if you took your finger and poked it, that is directional.
Now if you put your finger at the top of the apex of the symmetrical one, and pressed down, it squishes and produces 2 other curves, those are DISRUPTIVE.
Reply 4
Avatar for sahsum
sahsum
OP
13
thanks thats helpful, i had a read through another few books and i think i've grasped it!!
Reply 5
Avatar for ossoss87
ossoss87
3
I got an A in AS...what about u ?!? but am really scared from A2! specially unit 5.. cuz its soo boring, yuckh! s-cool is good but sometimes i find it not helpful.. can u send me (if u can) anynotes for photosynthesis or classifaction or genetic engineering?!
This is by far the most hated part of biology/human biology.

Luckily in biology you can forget about mathematcial means and call the mean average.

Stabalising selection, Think of a graph with average, a and standard deviation s. Stabalising, selection looses the extremities (stabalising LOVES the average) hence the "s" decreases. and the "a" remains constant.

directional selection, is when one of the extremities is favoured. hence the "a" will tend to the direction towards whichever extremitie is favoured.

disruptive selection is not fun. look at the graphs and imagine you push down the top of the curve. (disrupting the graph :O ) what this leads to is now 2 points. each with its own s and its own a.

I hope this is some help.
Reply 7
Avatar for sahsum
sahsum
OP
13
ossoss87
I got an A in AS...what about u ?!? but am really scared from A2! specially unit 5.. cuz its soo boring, yuckh! s-cool is good but sometimes i find it not helpful.. can u send me (if u can) anynotes for photosynthesis or classifaction or genetic engineering?!


I got a crappy C at AS, though that was foolishly with no revision. I did retakes in Jan and managed to do worse even with loads of revision that time. Clearly Bio was a mistake for me. But its wierd coz i do perfectly well in my other subjects?!?!?!Its not that i find it really hard to understand, i just don't see how it's possible to learn it all!!
I'm sure you won't fail if u got an A at AS!!

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