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    (Original post by ekta9)
    4th time?! Oh man im still on my first time round and havent even finished yet! Still got most of ecosystems and animal behaviours!
    dont worry... 113 hours left to go.... you can make it..
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    can someone pleaseeee pretty polly please explain to me about this dopamine drd4!!! i just dnt get what the books sayin
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    I F***in hate this unit. Full stop.
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    (Original post by greenford)
    dont worry... 113 hours left to go.... you can make it..
    This isn't reassuring
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    (Original post by heartskippedabeat)
    This isn't reassuring
    112 now

    :P
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    (Original post by Waqar Y)
    112 now

    :P
    I wish I didn't need sleep!
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    (Original post by heartskippedabeat)
    I wish I didn't need sleep!
    Don't we all, but tbh just try not to worry to much - the more you stress, the more you'll panic and forget.
    I keep thinking of impossible questions that are going to come up in the exam, and since i've dreamed impossible questions, i can't answer them LOL!
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    (Original post by Waqar Y)
    Don't we all, but tbh just try not to worry to much - the more you stress, the more you'll panic and forget.
    I keep thinking of impossible questions that are going to come up in the exam, and since i've dreamed impossible questions, i can't answer them LOL!
    Yeah i know, i try, i'm just a stressy person
    Haha that's not good! Knowing ocr, there probably will be an impossible question or three...
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    Anyone want to start a question/answer post thing up? Some one asks, another answers and asks another question and so on?
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    Im gonnna fail this unit and its cos of a few genes... I dont know nothing about genetics, module 1. Its going in one ear and coming out the other. What am i gona do.. 4 days left ((((
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    (Original post by ibysaiyan)
    Thanks.
    Past papers dating back to 01- (of the old spec from freeexampaper site)
    What exam codes would be the equivalent for F215 from the old spec? Thanks
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    (Original post by greenford)
    dont worry... 113 hours left to go.... you can make it..
    Yeah just 113 hours left to cover the last 2 modules.. fun. Also seeing as you've gone through it four times, could you explain recessive and dominant epistasis to me please
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    Yeah, i agree could someone cover Epistasis please. Whats all the blah blah about in those 2 spreads in the book.

    Thanks in advance
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    (Original post by ekta9)
    Yeah just 113 hours left to cover the last 2 modules.. fun. Also seeing as you've gone through it four times, could you explain recessive and dominant epistasis to me please
    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.
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    (Original post by ManPowa)
    Im gonnna fail this unit and its cos of a few genes... I dont know nothing about genetics, module 1. Its going in one ear and coming out the other. What am i gona do.. 4 days left ((((
    Think positive, read as much as you can, expect the worst but do your best, read through it make notes, the go back to bits and bobs etc, I think 4 days is more than enough for someone who has done it already, or at least has an idea of what unit 5 is all about,

    Hope this is reassuring

    Think POSITIVE
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    (Original post by Bullit)
    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.
    My teacher couldnt be bothered explaining it and there you do it with one example,

    GREAT
    thanks
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    (Original post by ekta9)
    Yeah just 113 hours left to cover the last 2 modules.. fun. Also seeing as you've gone through it four times, could you explain recessive and dominant epistasis to me please

    BULLT has explained it really well with an example....

    but in simple words...

    • Rominant epistaisis is when there is a dominant allele, which dominates all the other allele..no matter of they are dominant or recessive..


    eg. Allele C will result in white coat, not matter how many other allele's are present

    Recessive epistasis is when a recessive allele masks the expression for a dominat allele

    eg. allele A will mask the expression for allele B..

    sorry not very good at explaining...
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    (Original post by Bullit)
    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.
    Thank-you!!! Yeah you definitely explained it better than the book! I wrote down everything you said in my notes as it makes soo much more sense!
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    (Original post by greenford)
    BULLT has explained it really well with an example....

    but in simple words...

    • Rominant epistaisis is when there is a dominant allele, which dominates all the other allele..no matter of they are dominant or recessive..


    eg. Allele C will result in white coat, not matter how many other allele's are present

    Recessive epistasis is when a recessive allele masks the expression for a dominat allele

    eg. allele A will mask the expression for allele B..

    sorry not very good at explaining...
    Thanks!! I think I understand it now but need to do some past questions on it!
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    (Original post by ekta9)
    Thanks!! I think I understand it now but need to do some past questions on it!
    that's the best way to go...
 
 
 
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