OCR F215 - Stretch and Challenges A* Notes

This is a collection of notes regarding A* topics and ideas for the OCR F215 biology exam.

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  • Created by: Claire
  • Created on: 22-06-14 13:49
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F215 Stretch and Challenge ideas
Cellular control & genetics
> The degenerate code reduces the effects of substitution mutations
> If the nucleotide bases were arranged in pairs the maximum number of combinations would only be
16, which is not enough for the 20 amino acids plus stop codons
> Translation in prokaryotes is faster as they have no nuclear envelope - transcription takes places
straight away
> 'junk' DNA is misleading as it may have other purposes e.g. spindle fibres or chiasmata formation
which haven't been discovered yet
> Non disjunction explains polyploidy
> Humans prevent those without the traits from breeding in selective breeding
> If there are no mutations then there will be no genetic variation so natural selection cannot occur
> There are no centrioles or telophase I in plant cells
> Linkage: Genes are located on the same chromosome so there is no independent assortment of
chromosomes, and no chiasmata formation, a fewer number of recombinant gametes meaning the
genes are inherited together
> Directional selection takes place in changing conditions as the selection pressure changes
> Genetic drift is a change in allele frequency which occurs by chance, but the effects are large when
the gene pool is smaller as chance has a greater influence
> Might not be the same species because they cannot produce fertile offspring, are reproductively
isolated, have different physiology and morphology, and different genes
> Cladistics looks at monophyletic relationships as part of the phylogenetic species concept
> Selective breeding is carried out for the benefit of humans to produce desirable traits, increasing
the number of favourable alleles
> Several stages are needed in selective breeding as it's a gradual process to improve traits and
achieve homozygosity. The best in each generation are selected
> Progeny testing assesses the value of an individual's offspring for sex limited traits
> Polyploidy in wheat bread: Mitosis, chromosomes replicate, no spindle fibres so no cell division
> Sterile hybrid: 3n (odd chromosome number), homologous chromosomes cannot form, meiosis fails
Cloning, biotechnology & gene technology
> A clone is produced from one parent by asexual reproduction, by mitosis
> Tissue culture is expensive because of labour costs, sterile conditions and staff training
> In somatic cell nuclear transfer they may not be genetically identical because of the mitochondrial
DNA in the donor egg cell cytoplasm
> Somatic cell nuclear transfer is good because it doesn't require the species eggs, doesn't require a
fertile female, and the female isn't put at risk in pregnancy
> Secondary metabolites are produced to prevent competition as nutrient supply dwindles
> With continuous cultures there are problems with blocking of inlet/outlet pipes, contamination,
foaming and conditions need to be closely monitored which is time consuming
> Bacteria may not grow the same in real life compared to a lab because there is less oxygen,
different pH, interspecific competition from other bacteria and less nutrients
> Gene probes need to be short so they do not partially anneal
> Restriction enzymes are endonucleases from bacteria e.g. e.coli
> Restriction sites are specific, 4-6bp and palindromic
> Virus vector only effective once as we become immune, or they may cause illness
> Liposomes are inefficient, even more so when you try inserting more than one functioning allele
> Normal plasmids cannot penetrate cellulose cell walls so we use TI plasmids for plants
> cDNA has no introns so is shorter
> Bacterial plasmids are from bacteria such as e.coli

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Inserting a functioning allele may cause the trait to be over expressed, and it may be inserted in the
wrong place in the DNA or cause mutations
> Gene therapy can be an invasive process and there is a chance of rejection
> Gene therapy is no use for disorders where more than one gene is involved
> Energy is lost as heat from respiration, energy is lost at other levels
> Fungi damages the phloem and causes root rot, reducing NPP
> Although…read more

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Differences: Different sized wood produced, coppicing Vs felling, habitat destruction happens more
in large-scale production. Large scale reduces soil quality but coppicing does not, coppicing doesn't
involve planting new trees but large scale production does
Similarities: Selective cutting and growing standards are similar strategies to obtain high quality
Cellular control:
· Learn genetics definitions thoroughly.…read more

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I think:
Genetic variation (re assortment/ crossing over / mutation)
Apoptosis and cancer
Improving net primary productivity
The power stroke definitely (never come up before I think)
Asepsis (definitely how it can be done in labs etc.…read more


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