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    can someone please explain when it's referred to chromatin and chromosome

    is one X shape a bivalent and 2 X's a homologous pair with one from the mother and one from the father?
    is a bivalent the same as a chromosome?:/ ahh I'm so confused
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    wDo we need to know about interrupted succession and if yes what is it?
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    (Original post by cr7alwayz)
    How does apoptosis work
    Firstly the cytoskeleton is digested by enzymes+the cytoplasm then becomes highly condensed

    This causes the cell surface membrane to deform and start to bleb

    The Chromatin in the nucleolus then condenses + nuclear envelope breaks down

    Cell contents breaks up into fragments and packaged into vesicles + taken up by phagocytes
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    For genetic diagrams and the such, what are the ratios that we are expected to know?
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    (Original post by baymax96)
    can someone please explain when it's referred to chromatin and chromosome

    is one X shape a bivalent and 2 X's a homologous pair with one from the mother and one from the father?
    is a bivalent the same as a chromosome?:/ ahh I'm so confused
    Chromatin is just a complex of DNA and proteins in the nucleus most of the time except during division when it condenses and supercoils to form chromosomes which are visible under the microscope.

    During interphase, before nuclear division, DNA replicates and this is when the X shape forms as two sister chromatids are joined at the centromere.

    Then the bivalents form - homeologous pairs (the 2 same chromosomes with different alleles, one maternal and one paternal) joined together are bivalents. So 1 bivalent = 1 homologous pair = 2 pairs of sister chromatids.

    I'm not sure how clear this is but I hope it helps and if anything needs clarifying I'll be happy to try and help. Also is anyone sees something wrong please correct me
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    (Original post by baymax96)
    For genetic diagrams and the such, what are the ratios that we are expected to know?
    9:3:3:1 = dihybrid
    1:2:1 = codominance
    3:1 = monohybrid
    9:7 = complementary epistasis
    9:3:4 = recessive epistasis
    13:1 or 12:3:1 = dominant epistasis
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    (Original post by baymax96)
    For genetic diagrams and the such, what are the ratios that we are expected to know?
    Monohybrid cross- Ratio 3:1
    Dihybrid cross- 9:3:3:1
    Codominant- 1:2:1
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    Hey
    can someone please explain to me the phylogenetic species classification please. Thanks
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    (Original post by whenthecatcalls)
    Hey
    can someone please explain to me the phylogenetic species classification please. Thanks
    The study of the evolutionary history of groups of organisms. All evolve from common ancestors, the more closely related two species are, the more recently their last common ancestor will be. Problems with this are that there is no cut off as to when two organism are classed as different/same species. 94% of human and chimpanzee DNA is the same for example, but we are classed as different species
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    (Original post by anomolomon)
    I'm not sure if this has been posted, but I'm finding these videos really useful. He's got more good ones on his channel too. I'd definitely recommend checking them out if you're bored of the book!

    https://www.youtube.com/watch?v=7rqMzPlw79g
    ahh life saver! I was just starting to go through PCR as well haha thanks
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    any predictions for this exam? what is everyone focusing on?
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    (Original post by cforcoldplay)
    ahh life saver! I was just starting to go through PCR as well haha thanks
    I mostly use Bozeman or Khan academy
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    (Original post by cinderella25)
    I mostly use Bozeman or Khan academy
    OOh yes Bozeman science is great but i find it too generic. I got excited because this one's specific to OCR A2 bio. Haven't watched any of the Khan Academy ones
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    "Phenotype is influenced by genetic and environmental factors.Describe one example of how the environment influences phenotype".
    What examples are there? (Specimen question) The markscheme only says 'named example'.
    Thanks
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    Does anyone know why in the nuclear transfer articificial animal cloning process the early embryo is moved to a second surrogate mother? Why not just one surrogate?
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    (Original post by Shanahey)
    "Phenotype is influenced by genetic and environmental factors.Describe one example of how the environment influences phenotype".
    What examples are there? (Specimen question) The markscheme only says 'named example'.
    Thanks
    Accent is the suggested change in my revision guide. Its determined by environmental factors only, where you live, where you grew up and the accents of those around you
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    (Original post by Shanahey)
    "Phenotype is influenced by genetic and environmental factors.Describe one example of how the environment influences phenotype".
    What examples are there? (Specimen question) The markscheme only says 'named example'.
    Thanks
    I would choose human height. The environmental influence is nutrition; if a child doesn't consume enough protein, their full height potential won't be reached.
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    (Original post by jessicadanby1996)
    Accent is the suggested change in my revision guide. Its determined by environmental factors only, where you live, where you grew up and the accents of those around you
    (Original post by HeyThereHarry)
    I would choose human height. The environmental influence is nutrition; if a child doesn't consume enough protein, their full height potential won't be reached.


    Thank you! What would be an example for plants? I'm not sure whether the question is referring to plants or not
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    (Original post by E_149)
    Does anyone know why in the nuclear transfer articificial animal cloning process the early embryo is moved to a second surrogate mother? Why not just one surrogate?
    I haven't seen this mentioned before and can't think why! :eek:
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    (Original post by Shanahey)
    Thank you! What would be an example for plants? I'm not sure whether the question is referring to plants or not
    Plant height affected by light intensity and nutrient availability. however with this and the child example, you should note that the limit a organism can grow to (like height) is also controlled by genetics
 
 
 
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